The deterioration of substance abusers to the point where they need to be hospitalized generally happens slowly, over a period of years if not decades. During this time, most of their medical care takes place in an ambulatory setting. Primary care physicians are thus in an ideal position to identify and help patients in relatively early stages of the problem. The HMO, with its ability to practice patient-oriented case management and its access to all aspects of the medical care delivery system without additional financial burden to the patient, is particularly suited to provide effective and efficient care. The next challenge for HMOs is to reach patients at much earlier stages of their disease.