Integrating mental health services into primary care should improve the availability, access, and delivery of psychiatric care to the whole population. Health maintenance organizations (HMOs) are settings for the development of integrated medical-mental health services. This paper reports findings of a project to evaluate a team collaborative model in an HMO. In this model, primary care clinicians carry major responsibility for emotional problems of their patients, and mental health clinicians collaborate with and support primary care clinicians as well as treat referred patients. Over a two-year study period, 15.7 per cent of all patients who visited the HMO presented a mental or emotional difficulty. When psychotropic drug prescriptions were used as an unobtrusive measure for estimating underenumeration, this prevalence figure rose to 19 per cent. Primary care clinicians treated an increasing proportion of the emotional problem demand, although this increase could not be attributed only to the establishment of the team collaborative model. Findings concerning the psychiatric problems treated and psychotropic drugs prescribed by primary care clinicians are also presented. We conclude that the primary care clinicians did assume major responsibility for emotional problem treatment when encouraged and supported through the team collaborative process and other organizational arrangements.