In guinea pigs using testis homogenate with Complete Freund's Adjuvant as antigen, a close correlation between cellular immunity (CI) and orchitis injury was found. High titres of antisperm cytophilic antibodies (ACA) were found in serum simultaneously with gonadal lesions. Cytotoxic effects of ACA were investigated using a purified eluate of the antibody from macrophage surfaces and injecting it by subalbuginea route or incubating it with germinal cells or spermatozoa. The IgG2 nature of ACA was demonstrated by immunochemical techniques. Specific studies showed that the cytotoxic effect was not due to immune complexes. Ultrastructural studies of macrophage-ACA-spermatozoa complex by scanning and transmission electron microscopy showed the different stages of ACA-mediated sperm phagocytosis. "Thermal orchitis" was developed in guinea pigs as a model to induce orchitis without adjuvant. Isolation and identification of the sequential cell populations in the granuloma showed macrophages as the main cell type. T cells were seen to increase while B cells decreased and were substituted by plasma cells. Potentiality of unilateral sperm cord torsion for autosensitization against the other gonad was studied; orchiectomy of the injured gonad prevented the orchitis lesion and avoided the immune response. Infertile men were studied immunologically. Patients with genital infection or sperm duct obstruction exhibited positive antisperm autoimmunity tests. Cl alterations were detected early and persisted for many years, while humoral antisperm antibodies were not detected during more than two years. Azoospermic patients showed autosensitization in 50% of the cases. Finally, Percoll gradients were used to isolate and identify non spermatic round cells from semen samples of asthenozoospermic men.(ABSTRACT TRUNCATED AT 250 WORDS)