NEW YORK ( TheStreet) -- BlackRock ( BLK) was one of the more active stocks in after-hours action on Friday with shares of the New York-based asset manager set to be added to the S&P 500.

Standard & Poor's announced BlackRock would replace Genzyme ( GENZ) in the broad market index late Tuesday, sparking a three-day rally in the stock. The shares closed Friday at $202.43, up 0.7% for the day, and 8.5% since the news of its inclusion in the index hit the wire.

Volume has picked up as well with 18.7 million shares changing hands on Friday alone. Wednesday and Thursday saw volume of 4.6 million and 2.7 million respectively. The three-month trailing daily average for the stock is around 810,000.

Genzyme is being removed because of its pending acquisition by Sanofi-Aventis ( SNY). The deal is expected to close shortly.

Share of BlackRock ticked 52 cents lower to $201.91 in late trades, according to, with volume running above 5.3 million, trailing only Citigroup ( C) at 8.4 million, and AT&T ( T) on the Nasdaq's list of most actively traded New York Stock Exchange-listed stocks.

Genzyme was also seeing a good deal of attention in late trades, rising 14 cents to $76.15 on volume of more than 26 million, according to The trading is likely being spurred by fund managers who look to mirror the performance of the S&P 500 making moves to recalibrate their portfolios to reflect the changes.

BlackRock, which had an estimated $3.56 trillion in assets under management as of Dec. 31, has seen its shares rise 5.4% since the start of 2011 but the stock is still off 4.8% in the past year, and its 52-week high of $212.27 dates back to mid-April 2010.

Overall Wall Street is positive on the company, which has topped consensus profit views for its past eight quarters and trades at a forward price-to-earnings multiple of 14.3X. Of the 15 analysts covering the stock, 11 are at either strong buy (4) or buy (7) and the median 12-month price target sits at $223, implying 10%-plus upside from current levels.

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