NEW YORK (AP) -- U.S. stock market indexes briefly broke through major round-number milestones in early trading Monday.
The Dow Jones industrial average crossed 16,000 for the first time and the Standard & Poor's 500 index rose past 1,800 shortly after the market opened.
Within the next half-hour, though, both indexes had slipped below those levels.
Stocks have been rising sharply this year as the U.S. economy improves, companies report bigger profits and the Federal Reserve keeps up its easy-money policies.
The S&P 500 index has risen for six weeks straight and is up 26 percent so far this year. The market hasn't risen that much in a whole year since 2003.
The S&P 500 has closed above major round-number milestones three times this year: 1,500 on Jan. 25, 1,600 on May 3 and 1,700 on Aug. 1.
The S&P 500 was down less than a point, or 0.1 percent, at 1,797 as of 10:10 a.m.
The Dow was up 35 points, or 0.2 percent, to 15,996.
Boeing rose $4, or 3 percent, to $140, the most of the 30 stocks in the Dow. The plane maker booked $100 billion in orders at the opening of the Dubai Airshow.
Tyson Foods jumped $1.10, or 3.8 percent, to $29.86, the most in the S&P 500 index. The food company said its net income surged 41 percent in the latest quarter on higher sales of beef and chicken. The company raised its dividend 50 percent.
The yield on the 10-year Treasury note fell to 2.68 percent from 2.71 percent.