We report a new suppressor function of CD8+ CD57+ lymphocytes from HIV-seropositive patients recipients, on the cytolytic activity of allospecific CTL, NK and LAK cells. This inhibitory effect is mediated by a non-antigen specific soluble factor distinct from PGE2, TGF beta and TNF alpha and beta. Biochemical characterization indicates that the CD8+ CD57+ inhibitory activity: 1) is heat and trypsin resistant but remains sensitive to pronase E hydrolyse, 2) specifically bind to concanavalin A-sepharose column, 3) is mediated by a 20-30 kdaltons glycoprotein.