The frequency of endocrine abnormalities during the follicular phase in non-pregnant women with a history of recurrent abortion was investigated in a case-control study. A total of 42 consecutive women with recurrent spontaneous abortion (three or more consecutive abortions, mean +/- SD: 3.9 +/- 1.1 range 3-8) with no parental chromosome rearrangement or uterine abnormality were studied during the early follicular phase under standardized conditions. Serum concentrations of follicle stimulating hormone (FSH), luteinizing hormone (LH), prolactin, androstenedione, testosterone, dehydroepiandro-stenedione, 17-OH-progesterone, oestradiol, progesterone and thyroid stimulating hormone (TSH) were measured by commercially available radioimmunoassays. Controls were 42 nulligravid females with tubal or male factor infertility without miscarriage. Mean (SD) concentrations of prolactin and androstenedione were 14.2 +/- 6.7 ng/ml versus 10.5 +/- 3.5 ng/ml (95% CI 0.8-6.1) and 2.3 +/- 0.9 ng/ml versus 1.7 +/- 0.6 ng/ml (95% CI 0.2-0.9) in the study and control groups respectively. The other endocrine parameters were comparable in both groups. Obesity [BMI weight (kg)/height (m2) > or = 25] was more prevalent (23 versus 5 women, P = 0.0001) in the study than the control group. Recurrent spontaneous abortion is associated with abnormalities in prolactin and androgen secretion during the follicular phase, suggesting an endocrine aetiology in this disorder. Reduction of body weight and correction of hyperprolactinaemia and of hyperandrogenism may reduce the rate of miscarriage in a subsequent pregnancy in these women.