Cell-mediated cytotoxicity to 51Cr-labelled avian red blood cells coated by rabbit liver-specific lipoprotein was evaluated in 27 patients with untreated chronic active hepatitis (11 were HBsAg-positive). A significantly increased cytotoxicity was recorded in 10 of the 11 patients with HBsAg-positive chronic active hepatitis and in 13 of the 16 HBsAg-negative patients. The addition of rabbit LSP to the test system reduced to normal the cytotoxicity index in all the positive cases. Moreover, in order to evaluate the organ-specificity of cytotoxicity to rabbit LSP-coated cells, we added to the test system a macromolecular kidney protein fraction which was unable to block the cytoxicity in any of the positive cases. In 12 selected cases, which had previously shown an increased cytotoxicity to rabbit LSP-coated red blood cells, the incubation of their lymphocytes at 37 degrees C for 30 min in a plastic Petri dish resulted in the abolition of cytotoxicity. Our findings seem to indicate that cell-mediated cytotoxicity to LSP can also be detected with an antigen, not prepared from human liver. This is a further evidence that patients with chronic active hepatitis develop an immunological reactivity to not species-specific antigenic determinants in LSP.