The objective of our study is to determine whether aggressive tocolysis in patients with preterm premature rupture of membranes between 24 and 34 weeks gestation improves neonatal outcome. Patients with documented preterm premature rupture of membranes between 24 and 34 weeks gestation were prospectively randomized to group I, aggressive tocolysis with intravenous magnesium sulfate, or to group II, no tocolysis. The lecithin/sphingomyelin ratio was determined upon hospital admission and every 48-96 hours until delivery. Both groups received weekly steroids and antibiotics pending culture results and were promptly delivered when chorioamnionitis, fetal stress, or an Lecithin/sphingomyelin ratio of > or = 2.0 occurred. The study group involved 145 patients. No statistically significant differences between groups I (n = 78) and II (n = 67) were observed regarding demographic characteristics, gestational age at enrollment or at delivery, latency, development of clinical chorioamnionitis, birth weight, number of days in neonatal intensive care unit, days on oxygen or ventilatory support, frequency of hyaline membrane disease, necrotizing enterocolitis, intraventricular hemorrhage, neonatal sepsis, or neonatal mortality. Our data suggest that tocolysis in patients with preterm premature rupture of membranes does not significantly improve perinatal outcome.