Since Karim reported that prostaglandin F2a was effective in induction of labor various results were reported by many authors. Difference in results might be attributable to the difference in protocol method and dosage. This is the preliminary report to determine the optimal dosage and efficacy of prostaglandin F2a in induction of labor. In the present study prostaglandin F2a was administered by continous intravenous drip infusion to induce labor in 36 pregnant women at or over term. The results were as follows; 1. Vaginal deliveries occured in 13 patients (36.1%) and changes in pelvic score occured in 18 patients (50%) 2. Mean induction delivery time in primigravida was 8 hour 50 minutes and that in multigravida was 6 hour 8 minutes. 3. Neither uterine hypertonicity nor fetal bradycardia was observed and Apgar score in 1 and 5 minutes after delivery were similiar 4. Transient flushing nausea, vomitting and diarrhea were observed in 11 patients. Further studies are desirable for the determination of optimal dosase, efficacy and safety of prostaglandin F2a and to reduce the undesired effect in induction of labor