A 12-year-old Japanese girl and her mother showed insulin-resistant diabetes mellitus which was confmed by the response to an oral glucose load in both patients and by the small decrease in blood glucose after intravenous insulin in the daughter. Anti-insulin antibodies and anti-insulin-receptor antibodies were not detected in either patient. The circulating erythrocytes were found to have reduced insulin binding capacity, which, to judge from IDSo, was probably caused by decreased binding affhty of insulin receptors.The patients did not have acanthosis nigricans or signs of androgenization such as hirsutism, dysmenorrhea or polycystic ovaries. Endocrinological studies in the daughter showed elevated basal serum levels of luteinizing hormone (LH), dehydroepiandrosterone, testosterone and estrone, and an exaggerated LH response to LH-RH. It is possible that hyperinsulinemia caused by insulin resistance contributed to the increased secretion of LH and androgens, but it was unclear why signs of androgenization were absent in spite of increased secretion of LH and androgens.(ActaPaediatrJpn 1988; 30: 608 -614)