HMOs offer unparalleled opportunities as a setting for health promotion research while providing the health care system with direct and immediate benefits. The special advantages of doing health promotion research in an HMO include easy access to a large, relatively stable population; access to all aspects of the health care system; access to a unified, comprehensive medical record; and working within an organization that views health promotion activities as an essential part of its mission. This article reviews these advantages and illustrates how they have been used in a diverse series of research and demonstration projects conducted within the Northwest Region of Kaiser Permanente.