This study was designed to assess the relationship between psychopathology and serotonin generated prolactin response to clomipramine and to assess the relationship between improvement in psychopathology and prolactin levels. The experimental sample consisted of 15 patients in the drug and 12 patients in the placebo groups. Blood samples for prolactin levels were drawn at baseline, and at the end of 4,8, and 12 weeks. There were statistically significant differences in prolactin increase between the drug and the placebo groups at 4 but not at 12 weeks following treatment. When the four least improved and a similar number of the most improved patients were compared, the least improved patients had the most increase in prolactin and the most improved had the least increase.