The inhibition of labor subsequent to premature rupture of the membranes remains controversial. To evaluate the possibility that diminished amniotic fluid volume impacts on the latent period in patients receiving tocolytic therapy after premature rupture of the membranes, we reviewed our recent clinical experience with premature rupture of the membranes and the use of tocolytic agents. Between January 1985 and June 1988, 70 singleton pregnancies with premature rupture of the membranes between 25 and 34 weeks of gestation without prior tocolytic therapy were included. Ritodrine (n = 22), magnesium sulfate (n = 37), or both agents (n = 11) were administered and followed by oral terbutaline if tocolysis was achieved. Ultrasonographic examination was performed after admission and patients were grouped on the basis of estimates of residual amniotic fluid volume. Fourteen patients had adequate fluid volume; 20 had diminished fluid volume, and 36 had oligohydramnios. Patients with adequate fluid volume had a significantly longer interval between tocolytic therapy and delivery when compared with the other two categories (analysis of variance, p less than 0.001), and proportionately more patients remained undelivered for greater than 1 week (adequate 8 of 14 vs. diminished 3 of 20 and oligohydramnios 3 of 36; p less than 0.001). In the 18 patients with premature rupture of the membranes before 30 weeks' gestation, adequate fluid volume was associated with the longest latent period (adequate 14.0 days; diminished 12.6 days, and oligohydramnios 2.8 days; analysis of variance, p less than 0.05). We conclude that tocolytic therapy is of little benefit in the presence of oligohydramnios. If additional prospective studies of tocolytic efficacy in pregnancies complicated by premature rupture of the membranes are undertaken, inclusion of residual amniotic fluid volume as an independent variable before randomization should be considered.