The asymmetry of tritiated imipramine (IMI) binding sites (which are associated with serotonergic mechanisms) were investigated in the orbital frontal cortex in 6 women and men who died of natural causes, and who did not have a history of mental disorders. There was significant interhemispheric asymmetry in both sexes, higher B(max) on the right side compared with the left. The B(max) values of IMI binding in the right orbital cortex in women were significantly higher than in men. Our preliminary findings - gender difference of serotonergic mechanisms in some area of the human brain - are in accordance with the observed gender differences in a variety of serotonin-regulated behaviors (sexual behavior, aggression and impulse control), and serotonergic mental disorders (eating disorders, suicidal behavior, anxiety disorders and depression).