FORTUNE -- Warren Buffett has a piece of advice for Ben Bernanke: It's easier to buy than it is to sell.
Buffett, speaking on Saturday at Berkshire Hathaway's (brka) annual meeting in Omaha, said he is worried about what will happen when the Federal Reserve tries to wind down its recent efforts to stimulate the economy. Via a program nicknamed QE, short for quantitative easing, the Fed in recent years has bought up over $2 trillion in bonds in order to lower interest rates and promote borrowing and investment.
Some have warned that when the Fed decides to sell its trove of bonds, or even just stops adding to it, stock markets could tank. Rising interest rates could cause banks to lose billions, perhaps igniting another financial crisis. Buffett says we don't know what will happen, but he is concerned.
"QE is like watching a good movie, because I don't know how it will end," says Buffett. "Anyone who owns stocks will reevaluate his hand when it happens, and that will happen very quickly."
Buffett says he has enormous respect for Bernanke. And he says the economy, and Berkshire, have "benefited significantly" from quantitative easing. Low interest rates are allowing Berkshire to do deals it wouldn't have done in the past, he said, citing the recent Heinz deal. And he doesn't think low interest rates are discouraging banks from lending. He says he knows Wells Fargo (wfc), of which Buffett is a large shareholder, is doing everything it can to find borrowers.
Nonetheless, Buffett says the Fed's moves have the ability to cause a lot of inflation. And that it may not always be promoting the best decision making.
"People make different decisions when they can borrow for practically nothing," says Buffett. "It's a huge experiment."
Charlie Munger, Buffett's long-term chief lieutenant, who was also talking at the meeting, says he worries about more than just inflation.
"What has happened in macroeconomics has surprised pretty much everyone," says Munger. "Given that history, economists should be more cautious when they print money in massive amounts."