Stock market investors yesterday said enough is enough, sending Wall Street to its largest gain in history after eight punishing days that sent market indexes down more than 20 percent.

But if you're looking for logical explanation as to why investors who last week thought of Wall Street as a Dollar General store suddenly thought of it yesterday as a Nordstrom's having a 30 percent off sale, you're probably wasting your time.

How do you explain why the price tag on a share of Alcoa was $27 a month ago, $11.25 on Friday and $13.82 when the market closed yesterday? Or why Johnstown-based AmeriServ Financial went from being Friday's biggest loser to Monday's top performer?

"This is crazy. This is absolutely ridiculous," said Doug Kreps, a portfolio manager with Fort Pitt Capital in Green Tree.

Mr. Kreps made the assessment yesterday at about 1 o'clock, when the Dow Jones industrial average was up a mere 570 points. The index eventually closed at 9388, up 936, or 11 percent. The S&P 500 and Nasdaq registered similar gains.

The market's daily three-digit gyrations are so unpredictable that following the market's worst week ever, "we may end up with one of the best weeks in the market ever," Mr. Kreps said. "We just don't know."

AmeriServ closed yesterday at $2.40, up 81 cents. Local stocks topping Alcoa's 23 percent advance yesterday included Equitable Resources, which finished at $28.45, up $5.46; Koppers Holdings, up $5.55 to $25.59; and AK Steel, which closed at $14.20, up $3.17.

West View-based WVS Financial was the only local stock to decline, finishing at $16.27, down 99 cents.

The volatility has created a lot of fear and uncertainty on Wall Street. But most small investors by and large have not joined the stampede of panic-stricken investors who are selling stocks and moving the proceeds to what they perceive to be safer havens.

Through September, about 15 percent of the investors in 401(k) plans administered by Vanguard Group have shifted money in their accounts, according to Stephen Utkus of the investment's firm's Center for Retirement Research. "That means 85 percent have stuck with their original plan," he said. "Trading levels are up, but most people do not trade."

Hewitt Associates reports the 1.5 million investors in 401(k) plans it monitors are doing the same. The benefits consultant said that, through Friday, investors had moved about 1.1 percent of their 401(k) money -- or $1.2 billion of the $110 billion in the accounts that Hewitt analyzed -- from stocks to fixed income investments. That's more than the $921 million they shifted from stocks to bonds in September.

Investors in their late 50s and early 60s who had an above-average percentage of their 401(k) money in the stock market have been hurt the most in the past few weeks, Mr. Utkus said. But through Sept. 30, 47 percent of the investors in Vanguard-administered 401(k) plans had larger balances than they did at the beginning of the year. Many of those are younger workers who haven't been saving that long and whose contributions offset losses in their accounts, he said. Another 25 percent of 401(k) savers had balances that were reduced by 10 percent or less, he said.

"It's not like all of America is looking at huge losses," Mr. Utkus said. "Some are, and they're the ones getting a lot of attention."

He said that after the market's decline from 2000 to 2002, investors already in 401(k) plans by and large maintained their asset allocations -- the percentage of money they invest in stocks, bonds and other investments. But new workers who enrolled in a 401(k) plan after the bear market put less of their money in stocks. Mr. Utkus said the same thing could happen again.

"After what's just happened, you're going to be much more cautious than someone who enrolled [in a 401(k) plan] two years ago," he said.

The market roller coaster has made some investors realize that they were taking on too much risk, Mr. Kreps said. But Fort Pitt Capital clients who have done that realize that now is not the time to rectify it, he said. They'll rebalance their portfolios once the market recovers, he said.

Mr. Kreps offered this advice to investors who are cringing at the thought of looking at their third-quarter retirement account statements:

"I've not looked at my 401(k) portfolio in a week. It's invested where it needs to be invested over the next 20 years. Where it is over the next 20 days is not relevant."