Mental health services were included in comprehensive benefits available with no out-of-pocket expenses to enrollees in the Seattle Prepaid Health Care Project. This study was designed to examine the characteristics of users as compared to nonusers of mental health services and to examine the possibility of lower use of somatic health services attributable to the availability of mental health services. Two enrollee groups were studied: one group included enrollees with at least one mental health service (MH-U) and the other included those with some somatic utilization but without mental health utilization (MH-NU). Results indicated that mental health users were different from nonusers based on sociodemographic, health status, and prior utilization measures. Further, the mental health utilizers consumed more somatic services than other enrollees, even controlling for background variables. The visit and admission rates for the MH-U group were 2.4 times that of the MH-NU group, and total inpatient and outpatient costs were three times as high. On all three comparisons, approximately 60 per cent of the difference was accounted for by mental health utilization and by differences in sociodemographic and health status characteristics. The remaining 40 per cent could not be explained, but there is a suggestion that the higher utilization occurred for conditions where medical care is discretionary.