140 patients with a threatening premature birth at the greater than or equal to 24-less than 37 week of gestation were in this study randomly treated with hexoprenalin or salbutamol. In 77% in the hexoprenalin and in 74% in the salbutamol group the weight of the newborn was greater than or equal to 2500 g. In 66% in both study groups the birth occurred after the completed 37 weeks of gestation. During infusion of hexoprenalin tachycardia in mothers occurred statistically highly significantly less than during salbutamol. 11% of the mothers in the hexoprenalin group had side-effects during infusion compared to 30% in the salbutamol group. The correlation between the tocolysis-index (Baumgarten) and the prolongation-index (Richter) given by the regression lines facilitates in some measure the comparison of different tocolytic drugs concerning its tocolytic effect.