The present retrospective study investigates the effect of premature rupture of membranes on fetal neurocardiac maturation as reflected by the fetal heart rate (FHR) pattern. The FHR tracings of 41 cases involving premature rupture of membranes of at least 48 hours' duration at 24 to 37 weeks' of gestation were studied. Fifty-two cases of normal pregnancy who were matched for gestational age served as controls. The results demonstrate similar baseline FHR and variability in the study and control group. The incidence of FHR accelerations of 15 beats/min was significantly greater in cases of premature rupture of membranes, and their onset was detected at an earlier gestational age. In addition, the mean amplitude of FHR accelerations was significantly greater in the study group compared with the control group. As a result, patients with premature rupture of membranes have a reactive nonstress test at an earlier gestational age than do control patients. These findings support the concept that premature rupture of membranes causes accelerated neurocardiac fetal maturation, as reflected by FHR pattern, possibly by inducing a stressful intrauterine environment.