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Jan. 26, 2018
BLACKROCK FUNDS^SM BlackRock Health Sciences Opportunities Portfolio (the "Fund") Supplement dated May 17, 2018 to the Summary Prospectuses, Prospectuses and Statement of Additional Information ("SAI") of the Fund, each dated January 26, 2018, as supplemented to date The Fund currently operates as a diversified fund under the Investment Company Act of 1940, as amended. Accordingly, effective immediately, the following changes are made to the Fund's Summary Prospectuses, Prospectuses and SAI, as applicable: The last paragraph in the section of each Summary Prospectus entitled "Key Facts About BlackRock Health Sciences Opportunities Portfolio — Principal Investment Strategies of the Fund" and the last paragraph in the sections of each Prospectus entitled "Fund Overview — Key Facts About BlackRock Health Sciences Opportunities Portfolio — Principal Investment Strategies of the Fund" and "Details About the Fund — Principal Investment Strategies" are deleted in their entirety. The section of each Summary Prospectus entitled "Key Facts About BlackRock Health Sciences Opportunities Portfolio — Principal Risks of Investing in the Fund" and the sections of each Prospectus entitled "Fund Overview — Key Facts About BlackRock Health Sciences Opportunities Portfolio — Principal Risks of Investing in the Fund" and "Details About the Fund — Investment Risks — Principal Risks of Investing in the Fund" are amended to delete "Non-Diversification Risk."

Jan. 26, 2018

BLACKROCK FUNDS^SM
BlackRock Health Sciences Opportunities Portfolio
(the "Fund")

Supplement dated May 17, 2018 to the
Summary Prospectuses, Prospectuses and Statement of Additional Information ("SAI") of the Fund,
each dated January 26, 2018, as supplemented to date
The Fund currently operates as a diversified fund under the Investment Company Act of 1940, as amended. Accordingly, effective immediately, the following changes are made to the Fund's Summary Prospectuses, Prospectuses and SAI, as applicable:

The last paragraph in the section of each Summary Prospectus entitled "Key Facts About BlackRock Health Sciences Opportunities Portfolio — Principal Investment Strategies of the Fund" and the last paragraph in the sections of each Prospectus entitled "Fund Overview — Key Facts About BlackRock Health Sciences Opportunities Portfolio — Principal Investment Strategies of the Fund" and "Details About the Fund — Principal Investment Strategies" are deleted in their entirety.

The section of each Summary Prospectus entitled "Key Facts About BlackRock Health Sciences Opportunities Portfolio — Principal Risks of Investing in the Fund" and the sections of each Prospectus entitled "Fund Overview — Key Facts About BlackRock Health Sciences Opportunities Portfolio — Principal Risks of Investing in the Fund" and "Details About the Fund — Investment Risks — Principal Risks of Investing in the Fund" are amended to delete "Non-Diversification Risk."