Allocation to equities in the U.S. fell, with a net 19 percent of investors polled by the bank last week running underweight positions, in stark contrast to the overweight positions held in the first quarter of the year.
It comes after stock markets touched fresh highs, with the S&P 500 closing at record levels last week, when fund managers were polled. Equities have continued to climb this week, with the Dow Jones industrial average and S&P ending at new records on Monday.
The shift in exposure marks the single biggest monthly drop in fund manager allocation since September 2009, the bank said, with overweight cash positions rising sharply.
"There is no loss of faith in economic recovery, and positioning still assumes that the U.S. dollar goes up, but doubts are creeping in – hence this jump in allocation to cash," said Michael Hartnett, chief investment strategist at BofA Merrill Lynch Global Research, in a note.
Beyond the U.S., most investors remain broadly bullish on equities, but the number of managers in favor of stocks fell, with around 47 percent of respondents overweight - down 7 percentage points month-on-month.
Confidence in corporate profitability has also fallen, with only 7 percent of investors surveyed viewing the U.S. as the region with the most favorable earnings outlook.
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Despite the sharp adjustment in U.S. equity exposure, bonds were tipped to be the most vulnerable. Over half of the 208 investors surveyed, which collectively manage $608 billion, identified fixed income as the asset class likely to see the most volatility this year.
These shifts follow severe moves in bond markets, as investors weighed the timing of a Federal Reserve interest rate hike, as well as the duration of the European Central Bank's recently launched bond-buying program.
As well as downgrading U.S. stock holdings, investors bolstered their cash positions to 10 month highs, cut bond allocations and upped energy, technology and bank exposure according to the survey.