Actual intrauterine pressure (IUP) was measured continuously by the extraamniotic method for the monitoring of uterine contractions (UC) throughout the entire course of labor. As a result, it was found by using a PDP 11/60 minicomputer that the wave of intrauterine pressure levels includes signals below a frequency of 0.05 Hz and that a period of 10 minutes is suitable for averaging the levels of parameters of IUP which makes it possible to evaluate the average expulsive activity. A new data analyzing tocodynamometer with a digital low pass filter was developed based on the data mentioned above, and the average values for maximum active pressure, the UC area and UC interval were computed simultaneously. The data for these factors were digitally displayed and printed on recording paper at every UC time. These values were clinically useful for drawing the partograms and were available to use in trying to express the expulsive activity in simple "labor index" terms.