ABSTRACT: Experimental autoimmune vesiculoprostatitis (EAVP) was transferred within inbred Wistar rats by a relatively small number of spleen cells obtained 30 days after immunization of donors with MAG extract in CFA and injected in the internal jugular vein of recipients. Specific tissue alterations identical to those present in the glands of the donors were observed 7 days after the transfer of the cells. The main alteration present was infiltration of mononuclear cells in the interstitium accompanied by fibrosis in more severe cases and flattening of epithelium in the ventral and dorsal prostate, seminal vesicle, and occasionally in coagulating gland. Nine out of ten recipients developed sexual accessory glandular lesions of various degrees. No histological alterations were observed in the absence of cell-mediated immune response and extensive damage was only observed in rats expressing two or more positive assays. The separation of the transferred cells into enriched population of T and B cells has proved that T lymphocytes are required for the production of the tissue lesions. Depletion of T lymphocytes by nylon wool separation and anti-rat thymocytes serum and complement completely abrogate their capacity to transfer the glandular alterations. Furthermore, specific antibody precursor cells on their own seem to be incapable to promote the antibody synthesis and to initiate the glandular damage. We conclude that T lymphocytes are required for the adoptive transfer of specific tissue damage observed in autoimmune vesiculo-prostatitis as well as for the development of a cell-mediated immune response to MAG antigens. Whether the same or distinct T-cell subsets are involved in these two effects is discussed.