During the first stage of labour 48 parturients were treated with the tocolytic agent TH 1165 a (Fenoterol-hydrobromide) because of danger to the foetus. The product was slowly injected i.v. in doses of 50 mcg (35 pat.) and 25 mcg (9 pat.) and on 4 patients in doses of 35 mcg. We investigated the effects of this therapy on labour, on the mother's and the child's circulation and on the foetal acid-base balance and foetal gas partial pressure. Whilst the different TH 1165a doses were not markedly different in their tocolytic effect, we discovered that side-effects occurred considerably more often and more intensively when higher doses of TH 116A WERE ADMINISTERED. We therefore recommend one i.v. injection of 25 mcg TH 1165a for clinical uterine relaxation in emergencies during labour. To guard against a vena cava compression syndrome, the injection should always be given with the patient in a lateral position. In emergency uterine relaxation the cardiac tocography (supplemented if necessary by micro blood gas analysis) should be monitored. In order tnce-only syringe containing 25 mcg TH1165a.