Salomon rose 1/4, to 24 1/4, despite news that the Federal Bureau of Investigation had entered the investigation of possible trading violations by the firm.

Salomon Brothers announced yesterday the resignation of the law firm that had been conducting an internal investigation of the firm's trading violations in the Treasury securities market.

Paine Webber was ordered by the Big Board to pay $900,000 in fines for numerous sales and trading violations.

Companies Salomon announced the resignation of Wachtell, Lipton, Rosen & Katz, the law firm that had been conducting an internal investigation of the firm's trading violations.

Those reports said that agents of the Federal Bureau of Investigation had posed as brokers and secretly recorded trading-floor conversations as a way to detect trading violations.

The examinations in past years were rarely comprehensive and typically did not look behind the official fund books for evidence of trading violations in other documents, such as e-mail messages.

The New York Mercantile Exchange's chairman was asked to resign after charges of trading violations, but he refused.

As recently as early last week, prosecutors were telling subpoenaed traders that anyone found to have committed a trading violation would be charged with a crime.

The two have a history of trading violations.

Regulators also sent letters to fund managers that offer products in Luxembourg and have been accused of trading violations in the United States.