beta-Endorphin (beta-E) immunoreactivity was measured in the amniotic compartment of 52 normotensive and 45 hypertensive gestations. All the fetuses of the normal group were healthy and showed appropriate intrauterine growth, whereas only suffering and growth-retarded fetuses were included in the pathological group. As expected, amniotic beta-E concentration was found to be significantly higher in hypertensive than in normotensive pregnancies (mean +/- SEM: 129.1 +/- 8.15 vs. 59.1 +/- 2.68 pg/ml; p < or = 0.005). A positive correlation between the hormone levels and the diastolic as well as the mean maternal blood pressure (r: 0.554; p < or = 0.05 and r: 0.525; p < or = 0.05, respectively) was present only in pregnancies complicated by hypertension. Furthermore, a negative correlation (r: -0.555; p < or = 0.05) linked amniotic beta-E and the pulse pressure in normal but not in complicated pregnancies. Unless beta-E in the amniotic compartment is also of amniochorial origin, our results suggest that the fetal endorphinergic tone is either activated by elevated diastolic and mean maternal pressure levels or lowered by increased pulse pressure values in normally elapsing pregnancies.