The technology-focused Nasdaq was headed for one of its best days this year.
Apple, by far the biggest component of the index, climbed 9 percent after reporting that its earnings doubled from January through March. The company sold 35 million iPhones, twice as many as in the same quarter a year ago.
The surge made back about half of what Apple lost in the two weeks before its earnings announcement late Tuesday. One reason for the slump was an analyst's suggestion that Apple could not keep up the momentum in iPhone sales.
Stock in Apple, the most valuable public company in the world, hit $644 in intraday trading on April 10. It slid as low as $555 on Tuesday. In late morning trading Wednesday, it was up $50 at $611.
The gain helped power the Nasdaq up 56 points to 3,017. Apple makes up 12 percent of the Nasdaq, by far the biggest component.
The Nasdaq rose more than other market indicators thanks to its heavy weighting of Apple shares. The Nasdaq was up 2 percent versus gains of 1 percent in the broader Standard & Poor's 500 index of large U.S. companies and 0.6 percent for the Dow Jones industrial average.
The Dow, which does not include Apple, was up 82 points at 13,083. The S&P 500, which does, rose 15 points to 1,387. Apple makes up about 4 percent of the S&P.
Technology stocks in the S&P 500 rose 3 percent as a group, easily the best-performing industry in the market. Materials stocks and consumer discretionary companies were also having a strong day.
European markets also rose. Benchmark stock indexes were up 2.5 percent in Madrid and Paris, 2 percent in Frankfurt and 0.4 percent in London.
Apple may not be an economic bellwether, but it is "an important confidence indicator for the market as a whole, so these figures will help sentiment today," said Gary Jenkins, managing director at Swordfish Research in London.
The dollar and U.S. Treasury prices fell as investors moved money out of safe assets.
Among other stocks making moves:— Boeing rose 4.3 percent, the best performer among the 30 stocks that make up the Dow. Its first-quarter profit soared 58 percent. Airlines around the world are updating their fleets with more fuel-efficient planes.— US Airways climbed 1.9 percent. It raised fares to offset higher fuel prices and beat expectations for earnings. US Airways has won the support of unions at American Airlines, which is in bankruptcy protection, for a merger.— Harley-Davidson rose 5 percent. U.S. sales of the company's motorcycles jumped 26 percent in the first three months of the year, the fourth straight increase. The company credited the gain to a better U.S. economy and a restructuring program the company put in place four years ago.