Strategic Insight said Thursday that about $51 billion in net deposits was moved into stock funds and so-called hybrid funds, which invest in a mix of stocks and bonds - the most since $56 billion in January 2004.
On Thursday, stocks drifted lower as investors digested more earnings results and reports on the economy.
The Dow fell 49 points to 13,860.58. The S&P 500 dropped 4 points to 1,498.11, and the Nasdaq composite was little changed at 3,142.13.
The Dow is just 304 points from its all-time high.
Among companies reporting earnings Thursday, UPS Inc., the world's biggest package-delivery company and an economic bellwether, fell 2.4 percent to $79.29. The company's fourth quarter was hurt by weak global trade, and it forecast 2013 results below expectations.
Stocks have gained against a backdrop of low borrowing costs and a slow, but steady, economic recovery. However, the market may struggle to build on those gains as traders and investors turn their attention back to Washington, said Ernie Cecilia, chief investment officer at Bryn Mawr Trust.