Securities regulators are warning that some brokerages have "material weaknesses" in risk management procedures. Some firms had poor supervisory structures or used inappropriate risk measurement tools, the agencies said. They found that others did a good job of defining authorized activities and their limits, and employed experienced, and often independent, risk-management personnel.

The warning came in a statement by the Securities and Exchange Commission, the New York Stock Exchange, and the regulatory arm of the National Association of Securities Dealers. They formed a task force several years ago in the wake of huge losses involving securities trading.

Worries were reignited last September when financial markets were rocked by the near-collapse of Long-Term Capital Management, the highly leveraged hedge fund.

A spokesman for the Securities Industry Association said the industry does a good job of policing itself.

"The examples of a Long-Term Capital are extremely rare," he said.

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