Complete endocrinologic evaluation of 9 women (ages 24-41) with idiopathic melasma (melasma not associated with pregnancy nor ingestion of oral contraceptives) was performed and compared to age- and sex-matched normal controls. Serum cortisol, adrenocorticotropin, plasma immunoreactive alpha and beta melanocyte-stimulating hormones, luteinizing hormone, follicular-stimulating hormone, estradiol and progesterone levels were performed in the basal state. Additionally, total T4, T3RU, FTI, prolactin, 2-h postprandial blood sugar, and 24-h urine for 17-hydroxysteroids and 17-ketosteroids were done and found to be normal. The melasma patients presented statistically significant increased levels of LH (p less than 0.001) and lower levels of serum estradiol (p less than 0.025) than normal controls. It is proposed that these hormonal alterations may represent subclinical evidence of a mild ovarian dysfunction which may underlie the pathogenesis of some cases of idiopathic melasma.