Liver cell damages were inducible, when isolated liver cells coated with specific antibody against the liver cell membrane were cultured with peripheral blood mononuclear cells. Although this antibody-dependent cell-mediated cytotoxicity (ADCC) was induced by the closed contact of effector cells to targets via the specific antibody, a cytotoxic factor or factors causing the inhibition of protein synthesis in the liver cells was detected in the culture supernatant of the ADCC reaction. Similarly, peritoneal exudate macrophages activated by endotoxin lipopolysaccharide also exerted cytotoxic effects on the isolated liver cells by producing a cytotoxic substance or substances. These liver cell injuries induced by either the ADCC or activated macrophage culture supernatant were significantly reduced, when the isolated liver cells were pretreated with tritoqualine before adding the cytotoxic culture supernatants. These results suggest that tritoqualine may protect liver cells from immunological injuries.