The aim of this study was to evaluate the relationship of serotonin level after treatment with selective serotonin reuptake inhibitors in patients of unipolar depression and influence of serotonin on the secretion of prolactin. Twenty two depressed females of child bearing age, who had come for the first time in the Psychiatry Department were selected for this study. They were subjected to Hamilton rating scale and divided into mild, moderate and severe cases. Their urinary 5-hydroxy tryptamine (5-HT), 5-Hydroxy indole acetic acid (5-HIAA) and serum prolactin levels were estimated before and after 6 weeks of treatment with sero-tonin reuptake inhibitors. The treatment schedule decreased urinary 5-HIAA level signifi-cantly, but there was a non-significant increase in urinary 5-HT. There was also a slight in-crease in serum levels of prolactin. The results suggest that time period required for altera-tion in central neuronal serotonin may be longer than the duration of treatment with sero-tonin reuptake inhibitors.