Health insurance co-ops failed in Iowa

Hopes for co-ops may also be tempered by the experience of Iowa, home to Senator Charles E. Grassley, the senior Republican on the Finance Committee, which is trying to hash out a bipartisan health care proposal.

In the 1990s, Iowa adopted a law to encourage the development of health care co-ops. One was created, and it died within two years. Although the law is still on the books, the state does not have a co-op now, said Susan E. Voss, the Iowa insurance commissioner.

Wellmark Blue Cross and Blue Shield collects about 70 percent of the premiums paid in the private insurance market in Iowa and South Dakota.

To become established, a new market entrant would have to offer lower prices or better services, Ms. Voss said, adding: "Wellmark has a huge advantage. They already have contracts with practically every doctor in the state."