In full-term pregnant women, electrical and mechanical activity of the uterus was monitored throughout the course of labour promoted by intravenous infusion of Pg F2 alpha. The recorded potentials were mostly biphasic and characterized by their long duration ranging from 1 to 2s. A wide range of potential amplitudes (100 µV to 1.8 mV) was observed according to the various patients. Early at the beginning of labour induction, the electrical complexes firing at various uterine sites were proved to be in close relationship and also well correlated with the mechanical events. This feature remained unchanged during labour. Potential amplitudes also remained unchanged during the same period of time. Under these conditions, improvement of uterine coordination does not appear to be the mechanism by which the increase of uterine contractile strength, necessary to expel the fetus, is obtained at the end of gestation