Forty parturients underwent elective cesarean section under spinal anesthesia were divided into two groups of 20 each in this prospective randomized study. Group I received 100 µg of intrathecal morphine (ITM) mixed with 12 mg of 0.5% heavy bupivacaine (M100) while group II received 200 µg of ITM mixed with 12 mg of 0.5% heavy bupivacaine (M200). Two blood samples were taken from each patient for serotonin estimation, preoperatively and 4 hrs later. Postoperatively all patients were assessed for pruritus (incidence & severity), visual analog scale (VAS), first request of analgesia, and total analgesic dose required within 24 hrs.