We carried out a seroepidemiological study on 63 patients undergoing organ transplantation in order to determine viral markers like CMV, HTLV III, HS and V/Z. The antibodies valuation was carried out by enzyme-linked immunosorbent assays (ELISA-Abbott) and complement fixation test. All the tested markers give a high percentage of positivity even if the values relevant to anti-HTLV III antibodies can not be related to infection but, probably, to anti-HLA-Dr antibodies.