Serial changes in serum uric acid concentrations have been studied in a group of healthy women before conception, at regular intervals throughout pregnancy and finally 12 weeks after delivery. Compared with pre-pregnancy values uric acid concentrations decreased significantly by 8 weeks gestation and this reduced level was maintained until about 24 weeks. Thereafter the concentrations increased such that by term they were greater than the pre-pregnancy values in the majority of patients and remained elevated until at least 12 weeks after delivery. If clinical management during the second half of pregnancy is to be based on increases in serum uric acid concentrations then such increases will have to be carefully interpreted against the background of rising concentrations which occur as part of the physiological response to normal pregnancy.