With few buyers and sellers in the market, trading was volatile and the major indexes alternated between gains and losses, ending the day fractionally higher. The absence of broad-based selling led most traders to believe there had been only a limited reaction to the ricin concerns.

"I don’t think you can really attribute the choppiness to that," said Brian Williamson, an equity trader at The Boston Company Asset Management. "I think there aren’t a lot of stories out there in general about the economy and stocks themselves, so that slows things down a little bit."

According to preliminary results, the Dow Jones industrial average ended the day up 6.00, or 0.1 percent, at 10,505.18.

The broader gauges were also narrowly higher. The Nasdaq composite index gained 3.06, or 0.2 percent, to close at 2,066.21, after four days of declines. The Standard & Poor’s 500 index edged up 0.77, or 0.1 percent, to close at 1,136.03.

The discovery of a suspicious, powdery white substance in a Capitol Hill office late yesterday raised new concerns about terrorism on domestic soil and invoked memories of the anthrax attacks of 2001. The powder later tested positive as ricin, and all Senate office buildings were closed today.

The dollar was weaker against most other currencies today as fears about terrorism reverberated, and bonds moved higher. Gold prices rose.

As the last major fourth-quarter earnings trickled in, investors were trying to determine whether the largely positive results meshed with economic data. Some analysts said the market was still feeling the impact of last week’s statement from the Federal Reserve, which many interpreted as a signal that interest rates could rise sooner rather than later.

"We’ve seen the market take on a different personality day by day," said Stuart Freeman, chief equity strategist for A.G. Edwards & Sons. "But I think the biggest issue on the minds of investors is when is the Fed going to raise rates and when is the market going to rotate more in terms of sectors."

There have been hints that investors are slowly shifting their focus away from more speculative small-cap and tech stocks and into less risky, high-value blue chips, but there has not been a strong movement in that direction.

Gainers on the tech-heavy Nasdaq index included Cisco Systems, which closed 21 cents higher at $26.41 after Sanford Bernstein raised it to a "market perform" ahead of its earnings announcement after the market close. The networking company’s performance has been widely watched as an indicator of corporate technology spending.

Cisco’s earnings, reported after the market closed, beat Wall Street’s expectations by 1 cent a share on strong sales, but the company’s shares declined 1.33 percent in after-hours trading.