Passage of the 1973 Health Maintenance Organization Act (P.L. 93-222) represents a significant effort by the Federal government to experiment with organizational change in the structure of the health care delivery system. The history of the bill is briefly reviewed. The most important sections of the bill are analyzed from the perspective of an existing prepaid group practice plan. The author concludes that the bill contains sufficiently stringent requirements that it will not result in a major increase in the number of Health Maintenance Organizations unless similar requirements are imposed on other private insurance carriers. Furthermore, significant allowance for "phasing in" will be required for the existing prepaid group practice prototype plans to qualify for Federal certification.