This 1978 national survey of all operating Health Maintenance Organizations (HMOs) provided information on the current status of mental health services utilization and service coverage within HMOs. It achieved a 68 per cent response rate. Approximately 90 per cent (108) of the HMOs offered mental health services through basic or supplemental coverage plans; HMO organization characteristics reflected relative heterogeneity; the mean monthly costs for basic health plan coverage (physical and mental health services) were $33.85 (for individuals) and $95.15 (for families); HMOs reported lower physical and mental health hospital utilization and higher ambulatory utilization when compared to more traditional forms of health insurance coverage. The present coverage and uitlization of mental health services within HMOs reflect greater variability of benefits and utilization within HMOs. There is need for further studies of mental health utilization in relation to organizational structure and delivery pattern relationships within HMOs.