The treatment with Ritodrine of 38 women with preterm rupture of the membranes (PROM) and 109 with intact membranes (ITM) was compared. Before the 36th gestational week, parturition could be postponed significantly longer in the ITM group than in the PROM group (p less than 0.01), whereas there was no difference between the two groups after the 36th week. Parturition could be postponed significantly longer in the PROM group, when Bishop's score was below or equal to 6, than when it was above, while the same was true for ITM, when the score was even 9 or below (p less than 0.001). Therefore, it seems like that PROM adds 3 points to the Bishop score, when the score is used as a prognostic index for the ability to postpone parturition. There was no significant difference in the occurrence of RDS between the PROM group and the ITM group, although birth weight was significantly higher in the ITM group (mean 2799.5 g) than in the PROM group (mean 1985.5 g) (p less than 0.001). No serious side effects of the treatment given were seen, either in the mothers or in the infants. It is concluded that all women with preterm labor should be treated with ritodrine and bedrest, if betamethasone treatment of the mothers is indicated, as parturition could be postponed for at least 24 h in all pregnancies in both groups.