The field of consultation-liaison (C-L) psychiatry has developed a variety of research interventions to try to improve the recognition and treatment of mental disorders in primary care. The authors review the results of three generations of randomized trials of mental health interventions developed by C-L psychiatrists. In general, these trials have been more successful in improving detection of mental illness and increasing the application of mental health treatments by primary care physicians than in changing patient outcomes. The results of these randomized trials are interpreted by using models developed in the health services field.