Abnormal steroid secretion may contribute to anovulation in insulin dependent diabetic patients with amenorrhoea. We have measured serum sex hormone-binding globulin (SHBG) and free and bound oestrogen and androgen levels in 17 such patients. As controls we included 17 patients with insulin dependent diabetes mellitus and normal menstrual cycles, 21 regularly menstruating normal women (both sampled during early follicular phase), and 23 non-diabetic patients with amenorrhoea. The diabetic patients with normal cycles had significantly higher serum concentrations of delta 4-androstenedione and testosterone than the normal women (P less than 0.01). The amenorrhoeic diabetics in contrast had significantly lower serum concentrations of SHBG, 5 alpha-dihydrotestosterone and free and total oestradiol-17 beta than either group of menstruating women (P less than 0.05), and significantly lower concentrations of delta 4-androstenedione (P less than 0.01), dehydroepiandrosterone sulphate (P less than 0.01), testosterone (P less than 0.01), and oestrone (P less than 0.05), than the cycling diabetics. The two amenorrhoeic groups had similar free and bound sex hormone concentrations except that delta 4-androstenedione levels were significantly lower in the diabetics (P less than 0.01). We conclude that the low sex hormone levels in diabetic women with amenorrhea may be due to suppression of the hypothalamic-pituitary axis in view of the impaired LH secretion found in these patients and that excess androgen secretion seems not to be of aetiological importance in amenorrhea related to diabetes mellitus. The decreased steroid levels in amenorrheic diabetics is due to their suppressed ovarian function while the increased androgen levels in diabetics with regular cycles are probably of ovarian origin.