Investors liked what they heard from Ben Bernanke, and stocks rose enough to put them into positive territory for August.
The Federal Reserve chairman said on Friday morning that the Fed is ready to help the economy with more bond-buying.
The Dow Jones industrial average closed 90 points higher, up a half-percent at 13,090. The Standard & Poor's 500 index rose seven points to close at 1,406. The Nasdaq rose 18 points to almost 3,067.
Advancing stocks outnumbered decliners more than 2-to-1.
The Dow finished the month of August up by 0.8 percent. The S&P 500 rose more than 2 percent for the month, and the Nasdaq rose more than 4 percent.
Facebook set a new low. Downgrades by analysts pushed it down $1.03, or 5.4 percent, to $18.06.