The problem for the plaintiffs, experts said, is that many firms are defunct, have changed names, destroyed old records, or have been absorbed by other companies. In addition, it is sometimes difficult to document ties to the slave trade.

In the case of slave ships, for example, 19th-century marine insurance policies often didn't identify the cargo on board. Instead, the policy simply stated that it insured ''goods'' on board.

''What strikes me from what I know already is that the records do not say clearly that slaves were insured,'' said Ugo Nwokeji, assistant professor of history at UConn. ''We cannot say that we know it was widespread, although it is well possible that it would have been widespread.''

The insurance industry's connection to slavery is not a new revelation. It has been written about in publications like Mr. Blockson's 1977 book, ''Black Genealogy.'' Even on eBay, the Internet auction site, copies of slave life insurance polices are for sale. And the tale of the slave ship Zong, in which 133 sick slaves were thrown overboard in 1781 so the ship's owners could collect insurance, has been studied for years.

The connection has gained greater attention in recent years because of the research of Deadria Farmer-Paellmann, the lead plaintiff in the federal lawsuit that was filed on March 26 against Aetna, the FleetBoston Financial Corporation and the CSX Corporation. Ms. Farmer-Paellmann first stumbled across slave insurance policies in 1997 while researching a slave reparations paper for a law school class. After reviewing different courses of action, she decided to focus on corporations and private estates that had been involved in slavery.

''And that's how I came into Aetna,'' she said.

Ms. Farmer-Paellmann, who said she is a descendant of slaves, continued to pursue the issue long after her class ended. In 2000, she called Aetna and requested that they send her copies of their policies. She said she received two.

''I was really moved when I saw the policies,'' she said. ''It's one thing to read about it and it's another thing to actually see a copy of the policy, and it really caused me to pause. I have to say it was a very emotional experience.''