The tracings of intra-uterine pressure changes that are made during normal labours in primiparous patients, whether the labours were normal or accelerated with oxytocin, were analysed using a semi-automatic time-lag with the help of system of 25 parameters. The classical data of pressures and of time have been made up with a study of the minima and maxima of pressure measurements and the drawing up of new indices to characterise the pressure wave form. A study of the correlations between the different groups of parameters made it possible to make a summary of the information from a smaller number of data which were identical for the two groups of delivery. In particular working out the surfaces dose not seem to give extra information over and above that derived from a simple calculation of the length and intensity of the contractions. A comparative statistical study confirms that in accelerated labour there is a rise in the basal tone, in the maximum pressure and in the frequency of contractions, and shows a minimal scatter of the values obtained which demonstrated that oxytocin has a regulating effect. Using parameters for the shape of contractions, quite independently of the units chosen to measure, has made it possible to design a typical form for the graph for each group of labours.