Induction of labor is often necessary in patients with premature rupture of membranes. While the effect of oxytocin to stimulate labor is well established, it is potentially hazardous to both the mother and infant. In this study, castor oil was evaluated as a method to induce labor in uncomplicated patients at term gestation with premature rupture of membranes. A total of 196 patients with premature rupture of membranes was studied retrospectively. Of 107 patients who received castor oil, 75% went into labor as compared to 58% of 89 control patients who went into labor spontaneously (P < 0.02). On the basis of these results, it is concluded that castor oil, which is more economical and convenient than oxytocin, can be used safely and effectively to stimulate labor.