BACKGROUND: The aim of this study is to compare duration of analgesia and incidence of adverse effects between two doses of intrathecal morphine in patients after elective ceasrean section. METHODS: Group 1 (n = 31) received morphine 0.1 mg and group 2 (n = 28) received morphine 0.2 mg in addition to intrathecal dose of 2.0 ml of 0.5% bupivacaine in 8% dextrose and fentanyl 15ng. RESULTS: In both groups 1 and 2, excellent postoperative analgesia with long duration was obtained (19.4 +/- 10.1 and 20.5 +/- 11.3 hours, respectively). Fourteen patients (45.2%) in group 1 and 12 patients (42.9%) in group 2 developed mild pruritus that did not require treatment except one patient in group 2 who received nalbuphine 5 mg iv. Incidences of postopertaive nausea or vomiting were not significantly different between the two groups. CONCLUSIONS: Both small doses intrathecal morphine of 0.1 mg and 0.2 mg provided adequate analgesia and patient satisfaction postoperatively with same incidences of side effects.