The rapid growth of managed care poses challenges and opportunities for the health of the public. The fundamental risk is that both mission and accountability will be defined too narrowly; the opportunity lies in broadening both. What would a socially responsible managed care system look like? Such a system would provide excellent individual care to its enrollees, yet it would also include programs and activities that address broader populations and policies. We propose 8 attributes of such a system that can be used as a guide by managed care systems and to judge whether a managed care system is a responsible, accountable, and responsive contributor to the health of its community. As the role of the public sector shrinks, the private sector must expand its responsibility. It is both prudent and reasonable for managed care systems to seize their unique opportunity to improve the health of the public.