This study compares the extent to which need, predisposing, and enabling factors affect the use of mental health services in the specialty and general medical health sectors during a 6-month period. Data are drawn from the first wave of interviews of the Epidemiological Catchment Area (ECA) project at the Yale University site. The results indicate that 1) in the general population, factors affecting use of the two sectors differ; 2) among those using any mental health services, factors affecting use of the two sectors differ; 3) indicators of need have the strongest relationships with utilization; and 4) the effects of predisposing and enabling factors are contingent upon the presence of need.