New research from BlackRock shows that retail investors shunned the exchange-traded fund market—especially in U.S. equities—last month, despite increasing demand for most of 2013.
Daniel Gamba, head of BlackRock's iShares America, told CNBC's "Fast Money Halftime Report" on Tuesday how investors should interpret these numbers.
"Investors continue to use ETFs across the board to express their market views," Gamba said. "We had a negative June followed by a very, very positive July, which was close to $45 billion in inflows, and now we had $15 billion in outflows in August."
(Related: As market fell, investors moved toward risk)
Though the $15 billion represents the largest ETF one-month outflow on record, it is only about 1 percent of total ETF assets, he said. Outflows to total assets in June 2010 were larger on a relative basis, at 2.2 percent, he added.
Both equity and fixed-income ETFs saw money depart last month, while research showed bright spots in Europe and short-term fixed income. U.S.-focused equity ETFs took the majority of outflows, at $9 billion.
Despite the weak performance, the ETF market has been growing 10 percent to 12 percent this year, Gamba said, and the overall movement has been strongly positive. With more investors using ETFs in general, he said, "it's been more volatile."
New growth in the asset class is largely attributed to insurers, global money managers and international investors, Gamba added.
—By CNBC's Paul Toscano. Follow him on Twitter @ToscanoPaul