During hypoxia there is an increased formation of hypoxanthine from the consumption of ATP; simultaneously the oxidation into uric acid is decreased. The purpose of this study was to determine possible correlations between hypoxanthine concentrations in the amniotic fluid and states of fetal hypoxia. We obtained 83 amniotic fluid samples from 68 patients during pregnancy or delivery. Hypoxanthine was assayed fluorimetrically according to GARDINER [4]. In the course of pregnancy, hypoxanthine levels in the amniotic fluid rise slightly. A marked increase occurs during delivery (without labor mean = 3.4 +/- 0.9 mumol/l, with labor mean = 7.0 +/- 5.4 mumol/l, p less than 0.02). There is no significant difference in the levels obtained from the first and second stages of labor. In intrauterine fetal death (Fig. 1) and in depressed newborns (Tab. I) there were increased hypoxanthine levels in the amniotic fluid, this was not seen in other complications of pregnancy. Independently from the fetal state increased hypoxanthine concentrations may occur in the amniotic fluid evidently as a consequence of labor activity. Thus the determination of hypoxanthine levels in the amniotic fluid cannot be used for the diagnosis of fetal hypoxia.