Insulin and insulin-like growth factors have been implicated in the stimulation of ovarian steroidogenesis. To assess the effect of diabetes mellitus on this process, a comparison was made of progesterone production by cultured granulosa cells (50,000 cells/well) from 11 individual follicles of nondiabetic and 6 individual follicles of diabetic women. Diabetic metabolic control was fair [HbA1C 6.8, 8.7 (nl 5.0-7.5)]. Cells were collected by laparoscopic follicular aspiration after ovulation induction and isolated by Percoll gradient centrifugation. Progesterone production was measured after culture with hCG (10 IU/mL) or insulin (100 microU/mL). In both nondiabetic and diabetic groups on day 4, hCG significantly stimulated progesterone production (1,686 +/- 1,268 ng/mL to 4,123 +/- 2,825 ng/mL and 1,059 +/- 249 ng/mL to 1,506 +/- 245 ng/mL, respectively). In nondiabetic follicles, insulin also stimulated progesterone production on days 4 (2366 +/- 1032 ng/mL to 3699 +/- 1582 ng/mL; P less than .05) and 7 (987 +/- 475 ng/mL to 1858 +/- 929 ng/mL; P less than .05); this response was not noted in diabetic granulosa cells. We suggest that insulin-stimulated progesterone production by granulosa cells isolated in the presence of fair diabetic metabolic control is impaired.