Stocks ended an otherwise lackluster quarter on an upbeat note, as Janet Yellen said the Fed will maintain its "extraordinary" support for the economy for "some time to come" and as ECB officials say it may start easing to address the threat of deflation in the euro zone.
The S&P wound up with a 1.3% gain for March, the Dow's triple-digit gain today still left the index down 0.7% for the month, while the Nasdaq lost 2.5% in March even with today's 1% gain.
Leading the way was the beaten-down biotech sector, which has been hit hard in recent sessions; financials, industrials and techs also outperformed.
Trading volume was relatively light, with many sellers apparently stepping aside after unloading positions in recent sessions.
Treasurys ended flat, with the benchmark 10-year yield at 2.72%.