The S&P 500 set a new record close Thursday as buyers pushed up stocks helped by a cautiously positive view of the economy from Federal Reserve Chair Janet Yellen.
The Dow Jones Industrial Average added 74.24 points (0.46 percent) at 16,272.65.
The broad-based S&P 500 passed the previous high mark set in January with a gain of 9.13 (0.49 percent) to a record 1,854.29.
The tech-heavy Nasdaq hit its best level since the dot-com crash of 2000, finishing up 26.87 (0.63 percent) at 4,318.93.
Analysts credited Yellen, who said in testimony to a Senate panel that severe weather was responsible for some of the recent poor economic data.
But she added that the Fed is keeping its eyes out for signs of any fundamental shift in the growth picture, and that it could adjust its plan to wind up its stimulus program as needed.
"She seems to be very clear that if the economy turns for the worse, that the Fed would change their stand on the taper" of the huge stimulus program, said Peter Coleman, head trader at ConvergEx Group.
After the market's three-week downturn following the previous high, Coleman added, the fear of a significant correction "is kind of dissipating... and it looks like we are back on an uptrend."
Shares of long-struggling retailer JC Penney rocketed 25.3 percent after it said its turnaround was on track, posting 2.0 percent same-store sales growth in the fourth quarter and projecting "mid single digit" growth for all of 2014
Best Buy, the electronics retailer, started out the day with a 5 percent gain, as its quarterly earnings came in 22 percent above analyst estimates. But its forecast of slower sales in the first half sent the shares tumbling again, finishing the day with a 1.0 percent loss.
Reports that the National Highway Traffic Safety Administration opened a probe into General Motors's handling of a large auto recall sent the automaker's shares down 0.2 percent.
Among other major gainers, Apple added 2.0 percent and Verizon 2.5 percent.
Bond prices rose. The yield on the 10-year US Treasury fell to 2.64 percent from 2.67 percent, while the 30-year declined to 3.60 percent from 3.63 percent.