"The iShares MSCI Emerging Markets Fund has an excellent track record since its inception and a large base of investors who value its deep liquidity," Jennifer Grancio, head of iShares U.S. distribution at BlackRock, said in an e-mailed statement.

The firm has seen clients allocating money to country ETFs including its Brazil, Korea and Taiwan funds, as well as to domestic funds, said Christine Hudacko, a spokeswoman for BlackRock.

Country Funds

"Our suite of emerging market offerings, the largest in the ETF industry at $87 billion, has seen increasing flows into single-country funds, as investors become selective about their emerging market exposure," Grancio said. "This is a theme our investment strategists and others advocate as investors look to capitalize on the growth in emerging markets."

ETFs trade throughout the day like stocks and usually mimic indexes. Investors added $111 billion to U.S. ETFs last year, which pushed assets at yearend to $995 billion, according to Boston-based State Street.

BlackRock, based in New York, jumped into ETFs with its $15.2 billion acquisition of Barclays Global Investors in December 2009, which added the iShares funds. The world's largest money manager, BlackRock had $3.45 trillion in assets under management as of Sept. 30.

The firm had $450 billion in U.S. domiciled ETFs at the end of 2010, the most of any company, according to data compiled by State Street. State Street was second with $235 billion; Vanguard was third with $148 billion.

Winning Clients

Vanguard was initially reluctant to offer ETFs. Founder John Bogle criticized the product for encouraging short-term investing. In 2001, Vanguard introduced the Total Stock Market ETF, their first such product. Vanguard ETFs are separate classes of the firm's index mutual funds, a structure the company has patented.

Vanguard had $1.38 trillion in mutual-fund assets at the end of November, more than any other company, according to data from the Investment Company Institute, a Washington-based trade group. Investors added $40.3 billion to its ETFs last year, compared with $29.3 billion for BlackRock and $16.3 billion for State Street, according to State Street data.