Objective: To determine the efficacy of oral nifedipine as prophylaxis against uterine tachysystole associated with misoprostol induction of labor. Methods: A total of 116 patients undergoing induction with term, singleton pregnancies were enrolled. All patients received 50 μg misoprostol intravaginally every 4 h. Patients were randomly assigned also to receive nifedipine 10 mg orally every 4 h, or no prophylaxis. The primary outcome variable was the incidence of 12 or more contractions in any 20-min interval. Results: Data on 106 patients were available for analysis. There were 55 subjects in the misoprostol-nifedipine group and 51 controls. Nifedipine did not diminish the incidence of tachysystole when added to misoprostol (42% vs. 45% without nifedipine; p = 0.7). Conclusion:Prophylactic oral nifedipine was not shown to decrease the uterine tachysystole associated with vaginal misoprostol induction at a 50-μg dose.