The aim of this study was to verify to what extent danazol alters insulin sensitivity. To this end, insulin tests were performed before the application of danazol and during the last 15 days of a six-month treatment with this agent on nine women, from 21 to 37 years of age, who had endometriosis. The same test was also performed on nine healthy women, 21 to 35 years of age, in whom laparoscopy did not reveal endometriosis or other pelvic pathology. It was found that the total response of glucose to insulin was significantly lower in women with endometriosis during treatment with danazol than it was in the same women before the application of this agent or in normal women too. Our results support the view that danazol induces resistance to insulin.