The response of a short-term submaximal bicycle ergometer test on foetal heart rate (FHR) and on uterine activity was studied in 61 pregnant women between pregnancy weeks 32 and 40. 28 of the women had uncomplicated pregnancies, 13 were hypertensive, 11 were diabetic, and 9 had intrahepatic cholestasis of pregnancy. After exercise, FHR declined in healthy subjects in pregnancy weeks past 35, whereas no significant change was found in such subjects before week 35 of pregnancy. Analysis of variance revealed a difference of FHR between subjects with umcomplicated and pre-eclamptic pregnancies in relation to time (p = 0.021). Exercise induced uterine contractions in hypertensive subjects. Foetal bradycardia was found in 2 healthy, in 2 pre-eclamptic, and in one cholestatic subject. In healthy pregnant women a non-reactive FHR with concomitant reduced FHR variability was found after exercise (P less than 0.01). The FHR variability of patients with pathologic pregnancies was less affected. These results suggest that, after a relatively strenuous short-term exercise, foetuses of mothers with uneventful pregnancies can be at risk of hypoxia in late pregnancy, but the clinical significance remains uncertain.