A study was made of the pH value of uterine secretion in 100 women at the age of 18-50 years and with a normal menstrual cycle (28 +/- 2 days). Fifty women had inserted medicated IUDs (Copper T and Multiload Cu 250) and 50 women served as a control group. In the proliferation phase of menstrual cycle 22 women were with the IUDs (of whom 14 had group II and 8 women group III vaginal secretion) and 21 women without any IUD of whom 8 had group II and 13 women group III vaginal secretion. In the secretion phase 28 women were with IUDs, (8 had group II and 20 women group III vaginal secretion) and 29 women from the control group, of whom 17 had group II and 12 women had group III. For the sampling of the intrauterine fluid the aspiration method and for the pH determination the colorimetric method were used. It can be seen that there is no correlation between the group of vaginal secretion and the pH of the uterine fluid, that the presence of a medicated IUD induced an insignificant change in the intrauterine pH, and that the pH value of the uterine fluid ranges from 3.0-9.0 which may be an important factor in the elucidation of certain mechanisms that occur in the uterus in the presence of intrauterine devices.