Some of the decline in Bank of America's shares could come from trading by risk arbitragers, who trade in the shares of companies being acquired, Ms. Bush said.

The risk arbitragers, who can spot an uptrend in an avalanche and who command billions in ready cash, will begin testing the waters.

The winners are those who sold the "stub" shares that were to be left outstanding after the offer was completed, a group that includes many risk arbitragers.

That is a balance that is constantly being weighed by risk arbitragers, the professional investors who specialize in takeover stocks.

The consensus among several risk arbitragers who have consulted legal experts is that on strict antitrust grounds any objection to a Microsoft-Intuit merger is fairly weak.

Mr. Leach said risk arbitragers were sure to vote for Tyson, while institutions might split.

Hilton may have been the last great hope of the arbs, the takeover speculators who like to be known as risk arbitragers.

Although individual and institutional investors are still nursing their wounds from the October stock market collapse, Wall Street's risk arbitragers are back at the tables.

"There were a few hedge-fund types and some risk arbitragers who were playing the game," said one takeover trader, who spoke on condition of anonymity.

Some risk arbitragers invest in possible takeover candidates; most of them profess to avoid rumors and wait until a bid is announced and then assess the likelihood of its completion.