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 93 +/- 3.2 (mean +/- SEM) to 157 +/- 6.3 beats/min, and systolic blood pressure from 120 +/- 3.4 to 148 +/- 5.4 mmHg, but diastolic blood pressure was unchanged. Plasma concentrations of noradrenaline and adrenaline rose rapidly during the exercise, from 2.9 +/- 0.3 to 6.9 +/- 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 146 +/- 17 to 212 +/- 22 mg/ml, thereafter slowly declining. The serum concentration of cortisol remained unchanged. The mean concentration of oestriol rose from 31.5 +/- 2.6 to 33.9 +/- 3.0 nmol/l at least 5 min after the exercise, thereafter declining to 29 +/- 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.