Increased serotonin (2A) (5-HT(2A)) receptors have been reported in the postmortem brain of suicide victims. To examine if this increase is associated with the dysregulation of postreceptor sites in the signaling cascade, we determined [3H]phorbol dibutyrate (PDBU) binding to protein kinase C (PKC) in postmortem brain samples (Brodmann's areas 8 and 9) obtained from teenage suicide victims and control subjects. [3H]PDBU binding to PKC was determined in membranal and cytosolic fractions. We observed that B(max) of [3H]PDBU binding sites was significantly decreased in both membranal and cytosolic fractions in brain samples from Brodmann's areas 8-9 compared to matched controls. These results thus suggest that PKC may play a role in the pathophysiology of suicidal behavior.