Microsomal fractions were prepared from livers of normal mats and rats treated with 2-aminofluorene or 2-acetylaminofluorene as well as from hepatomas induced by feeding 2-acetylamino fluorene. The microsomes were solubilized with deoxycholate and examined by immunoelectmophoresis using rabbit antiserum

rat plasma and kidney microsomes. At least 9 precipitate arcs were detected with preparations from livers of normal rats. Similar patterns were obtained with preparations from livers of rats which had been injected with 2-aminofluorene or 2-acetylaminofluorene 72 hr earlier. In the latter case, at least 2—3 arcs were shown to fix anti-2azofluorene-'251 antibody, indicating that some microsomal components combined with the injected carcinogen. Some of the liver microsomal antigens including one of the carcinogen-binding components were not detected in prepara tions from livers of rats which had been fed 2-acetylaminofluorene for 16 weeks and removed from the carcinogen diet for 1, 2, or 4 weeks. Similar but more extensive changes in antigen composition were observed with preparations from hepatomas. Some anti gens, including the carcinogen-binding components, were not observed. In contrast, some antigens not clearly detectable in normal liver preparations were observed in hepatoma prepara tions. The role of the binding of carcinogen to the microsomal com ponents and the role of these components themselves in car cinogenesis remain to be seen.