Insider sales at American Express Co. and American International Group have dropped to almost nothing since September-a change in behavior that would be consistent with reports of merger talks between the two.

Until last fall, top executives and directors had been active sellers of their companies' shares. According to CDA/Investnet, Fort Lauderdale, Fla., a research firm that tracks insider stock transactions, insiders at American Express have sold an average of 317,000 shares annually since 1990, while AIG insiders have unloaded an average of 542,000.

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