AbstractElectron microscopic analysis of the distribution of H‐2 (b, d, k) antigens on the cell surface and viruses of Rauscher, Friend, Graffi, Mazurenko, Gross and SZ leukemia was carried out using the hybrid antibody test.H‐2 antigens occupied different areas on the surface of the cells, but their average content per 100 randomly selected cells ranged from 13‐24% in different leukemias. The amount of mature viral particles with H‐2 antigens on their surface did not correspond to the average content of these antigens on leukemia cells and amounted to 7‐15%. H‐2 antigens never covered the entire surface of viral particles and the ferritin label, which made it possible to spot them, was not more than 5‐7 molecules. The same was true of viral buds, the majority of which, even on membrane sites with H‐2 antigens, were devoid of these antigens. Possible reasons for the absence of H‐2 antigens on mature and budding viruses are discussed.