The move toward managed care initiatives and multiprovider networks has intensified in recent years in response to escalating healthcare costs and increasing market dominance by the insurance industry. As a consequence, the antitrust laws have played a significant role in defining the limits of physician cooperation. An understanding of the application of antitrust laws to evolving healthcare delivery systems and a knowledge of the specific areas where providers must exercise caution are essential to physicians' strategic planning. This article looks at the major areas of innovation emerging in the healthcare delivery market and details some of the most important guidelines for safeguarding physician collaborations. The authors compare the ability of physicians and insurers to organize integrated care systems and question the continued protection of the insurance industry under the McCarran-Ferguson Act.