The documented high incidence of mental health disorders among individuals in substance abuse treatment argues for the importance of studying the provision of mental health services to this population. This survey documents how the Linkage Programs assembled an array of mental health services based on the assessed health care needs of clients. Specialty and nonspecialty personnel addressed the extensive mental health needs of ethnically diverse, multiproblem clients with substance abuse problems. The innovative use of nonconventional providers, however, did not eliminate the shortfall between the number of clients with mental health problems and the number who were referred to and received mental health services; nor did it enable all Linkage Programs to address the mental health needs of the most severely ill clients. There is a continuing need to forge relationships between mental health providers and integrated providers of primary care and substance abuse treatment.