April 20, 2007

Supplement

SUPPLEMENT DATED APRIL 20, 2007 TO THE STATEMENT OF ADDITIONAL INFORMATION OF
MORGAN STANLEY DEVELOPING GROWTH SECURITIES TRUST
Dated January 31, 2007 

The following paragraphs are hereby added at the end of the section of the Statement of Additional Information entitled ‘‘II. Description of the Fund and Its Investments and Risks — B. Investment Strategies and Risks’’: 

    Stock Index Futures Contracts.    The Fund may purchase and sell stock index futures contracts that are traded on U.S. exchanges and on such indexes of U.S. and foreign securities as may exist or come into existence. 

    A futures contract purchaser incurs an obligation to take delivery of a specified amount of the obligation underlying the contract at a specified time in the future for a specified price. A seller of a futures contract incurs an obligation to deliver the specified amount of the underlying obligation at a specified time in return for an agreed upon price. The purchase of a futures contract enables the Fund, during the term of the contract, to lock in a price at which it may purchase a security and protect against a rise in prices pending purchase of portfolio securities. The sale of a futures contract enables the Fund to lock in a price at which it may sell a security or currency and protect against declines in the value of portfolio securities. 

    Index futures contracts provide for the delivery of an amount of cash equal to a specified dollar amount times the difference between the index value at the open or close of the last trading day of the contract and the futures contract price. A futures contract sale is closed out by effecting a futures contract purchase for the same aggregate amount of the specific type of security and the same delivery date. If the sale price exceeds the offsetting purchase price, the seller would be paid the difference and would realize a gain. If the offsetting purchase price exceeds the sale price, the seller would pay the difference and would realize a loss. Similarly, a futures contract purchase is closed out by effecting a futures contract sale for the same aggregate amount of the specific type of security and the same delivery date. If the offsetting sale price exceeds the purchase price, the purchaser would realize a gain, whereas if the purchase price exceeds the offsetting sale price, the purchaser would realize a loss. There is no assurance that the Fund will be able to enter into a closing transaction. 

    Margin.    If the Fund enters into a futures contract, it is initially required to deposit an ‘‘initial margin’’ of cash, U.S. government securities or other liquid portfolio securities ranging from approximately 2% to 5% of the contract amount. Initial margin requirements are established by the exchanges on which futures contracts trade and may, from time to time, change. In addition, brokers may establish margin deposit requirements in excess of those required by the exchanges. 

    Initial margin in futures transactions is different from margin in securities transactions in that initial margin does not involve the borrowing of funds by a broker’s client but is, rather, a good faith deposit on the futures contract, which will be returned to the Fund upon the proper termination of the futures contract. The margin deposits made are marked-to-market daily and the Fund may be required to make subsequent deposits of cash, U.S. government securities or other liquid portfolio securities, called ‘‘variation margin,’’ which are reflective of price fluctuations in the futures contract. 

    Risks of Transactions in Securities Index Futures Contracts.    The prices of indexes subject to futures contracts (and thereby the futures contract prices) may correlate imperfectly with the behavior of the cash prices of the Fund’s portfolio securities (and the currencies in which they are denominated). Also, prices of futures contracts may not move in tandem with the changes in market movements against which the Fund seeks a hedge. A correlation may also be distorted (a) temporarily, by short-term traders’ seeking to profit from the difference between a contract or security price objective and their cost of borrowed funds; (b) by investors in futures contracts electing to close out their contracts through offsetting transactions rather than meet margin deposit requirements; (c) by investors in futures contracts opting to make or take delivery of underlying securities rather than engage in closing transactions, thereby reducing liquidity of the futures market; and (d) temporarily, by speculators who view the deposit requirements in the futures markets as less onerous than margin requirements in the cash market. Due to the possibility of price distortion in the futures market and because of the possible imperfect correlation between movements in the prices of securities and movements in the prices of futures contracts, a correct forecast of market movement trends by the Investment Adviser may still not result in a successful hedging transaction. 

    There is no assurance that a liquid secondary market will exist for futures contracts in which the Fund may invest. In the event a liquid market does not exist, it may not be possible to close out a futures position and, in the event of adverse price movements, the Fund would continue to be required to make daily cash payments of variation margin. 

    Exchanges also limit the amount by which the price of a futures contract may move on any day. If the price moves equal to the daily limit on successive days, then it may prove impossible to liquidate a futures position until the daily limit moves have ceased. In the event of adverse price movements, the Fund would continue to be required to make daily cash payments of variation margin on open futures positions. In these situations, if the Fund has insufficient cash, it may have to sell portfolio securities to meet daily variation margin requirements at a time when it may be disadvantageous to do so. The inability to close out futures positions could also have an adverse impact on the Fund’s ability to effectively hedge its portfolio. 

    Futures contracts which are purchased or sold on foreign commodities exchanges may have greater price volatility than their U.S. counterparts. Furthermore, foreign commodities exchanges may be less regulated and under less governmental scrutiny than U.S. exchanges. Brokerage commissions, clearing costs and other transaction costs may be higher on foreign exchanges. Greater margin requirements may limit the Fund’s ability to enter into certain commodity transactions on foreign exchanges. Moreover, differences in clearance and delivery requirements on foreign exchanges may occasion delays in the settlement of the Fund’s transactions effected on foreign exchanges. 

    In the event of the bankruptcy of a broker through which the Fund engages in transactions in futures, the Fund could experience delays and/or losses in liquidating open positions purchased or sold through the broker and/or incur a loss of all or part of its margin deposits with the broker. 

    If the Fund maintains a short position in a futures contract, it will cover this position by holding, in a segregated account maintained on the books of the Fund, cash, U.S. government securities or other liquid portfolio securities equal in value (when added to any initial or variation margin on deposit) to the market value of the securities underlying the futures contract or the exercise price of the option. Such a position may also be covered by owning a portfolio of securities substantially replicating the relevant index, or by holding a call option permitting the Fund to purchase the same contract at a price no higher than the price at which the short position was established. 

    In addition, if the Fund holds a long position in a futures contract, it will hold cash, U.S. government securities or other liquid portfolio securities equal to the purchase price of the contract (less the amount of initial or variation margin on deposit) in a segregated account maintained on the books of the Fund. 

PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE.