The hormonal responses to exercise during later pregnancy were studied in relation to an exercise test in ten healthy women. At the end of the 10-min exercise, maternal heart rate had risen from 9 3 i 3 -2 (meankSEM) to 157k6.3 beats/min, and systolic blood pressure from 120k3.4 to 148k5.4 mmHg, but diastolic blood pressure was unchanged. Plasma concentrations of noradrenaline and adrenaline rose rapidly during the exercise, from 2 . 9 k 0 . 3 to 6 . 9 k 1 -2 nmol/l and from 0,31+0.04 to 0,47+0.08 nmol/l respectively. The serum concentration of prolactin did not change during the test, but 30 min after the exercise the value had risen from 146k17 to 212k22 mg/ml, thereafter slowly declining. The serum concentration of cortisol remained unchanged. The mean concentration of oestriol rose from 31.5k2.6 to 3 3 . 9 k 3 . 0 nmol/l at 5 min after the exercise, thereafter declining to 2 9 k 2 . 6 nmol/l. After the test. levels of progesterone and oestradiol also fell slightly. Mild irregular uterine activity was found in four subjects. Cardiotocography revealed a transient fetal tachycardia in two subjects.