PROBLEM: The aim of this study was to investigate the influence of immune-activated testicular macrophages obtained from rats with autoimmune orchitis (EAO) on Leydig cell steroidogenesis. METHOD OF STUDY: EAO was induced in rats by active immunization with testis homogenate and adjuvants. Testicular and peritoneal macrophages from rats with EAO were isolated and cultured for 24 hr. Testosterone (T) production by purified Leydig cells incubated in vitro with macrophage-conditioned media (CM) from rats with EAO or control rats was measured. RESULTS: An increase in T production by Leydig cells incubated with CM from testicular, but not peritoneal, macrophages of rats with EAO was observed. This increase was dose-dependent up to a concentration of 30% CM; proportions higher than 35% exhibited an inhibitory effect. CONCLUSIONS: Immune-activated testicular macrophages obtained from rats with EAO induced both stimulatory and inhibiting steroidogenic effects on Leydig cells in vitro and not the exclusively inhibitory action that has widely been attributed to activated macrophages. This dual effect probably depends on the ability of these cells to synthesize different molecules that may exert opposite effects.