The metabolic state of peritoneal macrophages is defined quantitatively for spontaneous ROI release and compared with those produced after cell contact with phorbol myristate acetate (PMA) or zymosan (OZ) particles. Peritoneal exudate cells (PEC) from EAP animals spontaneously released significantly more ROI than cells from controls rats, indicating that mononuclear phagocytes from autoimmune rats were more activated than populations cells arising from rats injected with BSA, with CFA or non-injected. These findings could indicate anin vivoactivation state in PEC from autoimmune rats different from that obtained with heterologous antigens or CFA immunization procedures. The release of ROI induced afterin vitrostimulus was, in general, higher in cells from autoimmune than in BSA or CFA treated rats.This differential responsiveness between the MAG, BSA and CFA injected macrophage populations could indicate that during the autoimmune process the autoantigen/s could amplify the inflammatory response triggered by them.Although release of oxygen metabolites represents only one of many potential mechanisms of tissue injury, this together with the lesions observed in the prostate gland indicate that oxygen radicals could be involved in this autoimmune disease.