Acute and chronic infectious prostatitis are the best understood of the prostate syndromes, but they are the least frequent. In contrast, although chronic non-infectious prostatitis is the most frequent syndrome, its cause has proved elusive despite years of investigation. In the present study, we analyzed a group of patients with infectious and non-infectious chronic prostatitis in order to search for the presence of a possible autoimmune response to prostate antigens. We demonstrated the presence of lymphocytes able to proliferate in response to known human prostate antigens such as PSA and PAP only in a group of patients with non-infectious chronic prostatitis. We observed that, as in other autoimmune diseases, a proliferative response against two or more autoantigens was a common feature. Moreover, when INFgamma and IL-10 levels were measured in culture supernatants, significantly elevated levels of INFgamma were detected only in samples from patients with positive proliferative response to prostate antigens. Interestingly, only these patients showed significantly elevated levels of inflammatory cytokines (IL-1 and TNF-alpha) in seminal plasma, arguing for a local inflammation of non-infectious cause. Our results show that INFgamma-secreting lymphocytes specific to prostate antigens are in fact detected in 34% of the patients with chronic non-infectious prostatitis. We speculate that these cells could be involved in the inflammatory process taking place in the prostate gland and therefore could alter its biological function.