ObjectiveTo compare the efficacy of nifedipine with ritodrine in the management of preterm labor.MethodsOne hundred eighty-five singleton pregnancies with preterm labor were assigned randomly to either ritodrine intravenously (n= 90) or nifedipine orally (n= 95). The principal outcome assessed was delay of delivery.ResultsRitodrine was discontinued in 12 patients because of severe maternal side effects, and their results were excluded from further analysis. More women in the ritodrine group delivered within 24 hours (22 versus 11,P= .006), within 48 hours (29 versus 21,P= .03), within 1 week (45 versus 36,P= .009), and within 2 weeks (52 versus 43,P= .005) compared with those receiving nifedipine. There were significantly fewer maternal side effects in the nifedipine group. Apgar scores and umbilical artery and vein pHs were similar in both groups. The number of admissions to the neonatal intensive care unit (NICU) in the nifedipine group was significantly lower than in the ritodrine group (68.4 versus 82.1%,P= .04).ConclusionNifedipine in comparison with ritodrine in the management of preterm labor is significantly associated with a longer postponement of delivery, fewer maternal side effects, and fewer admissions to the NICU.