In view of the connection which exists between premature birth and placental insufficiency and the means which are available for determining the respiratory performance of the fetoplacental unit by way of cardiotocography, the authors investigated the incidence of prepathological findings in the fetal heart frequency parameters for 81 cases of imminent premature delivery before, during and after intravenous tocolysis, and for 10 normal pregnancies between the 28th and 36th week. The greater number of prepathological cardiotocograms (oscillation amplitude and frequency, periodic acceleration and deceleration) found at the beginning of a trend toward premature delivery beginning with the 30th week of pregnancy, confirms the assumption of a restricted respiratory function of the fetoplacental unit. This restriction is, however, slight. The increase which is observed in these changes, particularly during up to 7 days of intravenous tocolysis in the 28th/29th week of pregnancy, and which continues after the end of intravenous therapy in the further course of pregnancy, is not seen as a result of the effect of betamimetics. The latter obviously do not succeed in positively influencing respiratory insufficiency in the event of imminent premature delivery. Neither the cardiotocographic findings from the beginning of the therapy nor later results permit conclusions to be drawn with regard to its possible success. On the other hand, a prepathological finding, especially where this occurs immediately before delivery, suggests possible larger disturbances of respiratory performance intrapartum, and problems with neonatal adaptation.