This article reviews the research literature on referral to and consultation with mental health specialists for patients in ambulatory medical settings. Very few controlled trials measuring the efficacy of such liaison could be located. They were mainly from the British literature, usually involved psychologists, and (with the exception of one study) tested only the model of referral to the mental health specialist for treatment. More research needs to be done in this important area. Methodologic issues and topics for further study are discussed.