The aim of this study was to verify to what extent danazol alters cell-mediated immunity. To this end, cell-mediated immunity was studied in 10 infertile patients with endometriosis and in 10 normal controls. Nonspecific parameters studied included serum SIL-2R, IL-6 and IL-1a levels. We also investigated the effect of treatment with Danazol on the levels of SIL-2R, IL-6 and IL-1a in women with endometriosis. Blood SIL-2R, IL-6 and IL-1a levels were measured in endometriotic women before treatment, during the last fifteen days of a 6-months course of Danazol and three months after treatment. Only one blood sample was taken from 10 women without endometriosis. SIL-2R, IL-6 and IL-1a levels were higher in women with endometriosis before treatment compared with controls. Administration of the drug significantly reduced the levels of SIL-2R (P < 0.001), IL-6 (P < 0.05) and IL-1a (P < 0.01). Our findings suggest that endometriosis is a condition which induces a rise in interleukin levels. Danazol also appears significantly to reduce endometriosis-associated autoimmune abnormalities.