Androstenediol (5-androsten-3β, 17β-diol, ADIOL) and androstenediol 3-sulfate (ADIOLS) are active metabolites of dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS), respectively, and have estrogenic activity and immunoregulatory function. We examined serum concentrations of ADIOL, ADIOLS, DHEA, DHEAS and pregnenolone sulfate (5-pregnen-3β-ol-20-one sulfate, PREGS) in patients with Graves' thyrotoxicosis (male/female 9/14), hypothyroidism (11/20) and in normal controls (14/29). In hypothyroidism serum levels of all these steroids were significantly decreased in both genders. In hyperthyroidism, in contrast, serum levels of ADIOLS (male 1.49±0.69, female 0.64±0.31μmol/l), DHEAS (male 7.43±3.91, female 5.13±2.03μmol/l), and PREGS (male 1.13±0.58, female 1.07±0.85μmol/l) were markedly increased, but serum concentrations of ADIOL and DEHA were not significantly different from controls (ADIOLS male 0.36±0.33, female 0.14±0.09μmol/l; DHEAS male 2.88±1.70, female 1.86±1.03μmol/l; PREGS male 0.18±0.12, female 0.11±0.08μmol/l; ADIOL male 3.76±1.35, female 1.91±1.17nmol/l; DHEA male 9.23±3.49, female 13.5±10.8nmol/l). Serum concentrations of all these steroids correlated with the serum concentration of the thyroid hormones in these patients. Serum albumin and sex hormone-binding globulin concentrations were not related to these changes in the concentrations of steroids. These findings indicate that serum concentrations of ADIOLS, ADIOL, DHEAS, DHEA and PREGS were decreased in hypothyroidism, whereas serum ADIOLS, DHEAS and PREGS concentrations were increased but ADIOL and DHEA were normal in hyperthyroidism. Thyroid hormone may stimulate the synthesis of these steroids and sulfotransferase is speculated to be increased in hyperthyroidism. Increased ADIOLS might contribute to menstrual disturbances and gynecomastia in hyperthyroidism.