Massive health care consolidation during the 1990s reduced the number of competing hospitals, insurers, and physician organizations in many markets. Some observers say that this period of intense merger-and-acquisition activity squeezed excess capacity out of the health care system, increasing its efficiency. Nevertheless, concerns have arisen with respect to anticompetitive behavior - actions that adversely affect competition and thus price or service quality - among hospitals, insurers, and physician organizations.

In response, Deborah Haas-Wilson, Ph.D., a professor of economics at Smith College, says she believes in the power of competitive health care markets, and in the capacity for antitrust enforcement to monitor those markets. "It has become increasingly important to make sure that health care markets are functioning well," she says. "Some government regulation is necessary, but in most cases the tool of choice is active but careful antitrust enforcement."

The trick, Haas-Wilson says, is that antitrust enforcement "must be neither too vigorous, nor too lenient." It has to be just right.