In 37 pregnancy women preterm labour was inhibited with intravenous administration of ASA. 20 patients (Group I) had a combined treatment of ASA and Fenoterol. 7 pregnant women (Group II) without successful labour inhibition under Fenoterol were treated with ASA subsequently. In a third group of 10 women we administered ASA alone. The treatment was considered as successful if signs of preterm labour stopped and pregnancy maintained for 7 days or more. In the first group 16, in the second group all patients had been treated successfully. In group III we succeeded in labour inhibiting for more than 7 days in 6 cases. An initial loading dose of 5.5 to 7.0 mn/min ASA had been infused for 24 hours. If preterm labour was stopped, the dosage had been reduced. In all patients dose related but reversible symptoms of vertigo, tinnitus, headache and hyperventilation were seen. Furthermore we found a non-dose-dependent prolongation ( by 30% or normal) of bleeding time. In the fetus respectively the newborn an affection by this ASA treatment could be excluded. We propose inhibition of preterm labour by i.v. ASA administration in all pregnant women if beta-mimetic drugs are not successful or an intolerance is diagnosed. Contraindications for ASA therapy are mentioned.