The Securities and Exchange Commission has sent at least three dozen subpoenas to hedge funds and brokerages within the past month in an expanding sweep of potential insider-trading violations, according to people familiar with the matter.

At least some of the inquiries are focused on potential information leaks around health-care mergers of the past three years, these people said. Some retail-industry deals also are a subject of the SEC inquiries, these people said, including Sears Holdings Corp.'s aborted pursuit of home-furnishings retailer Restoration Hardware in 2007.

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