The early region of the polyoma genoma encodee three T antigens. We have analyzed the organizetion of the coding regione for the T antigens, using the nucleotide sequence of polyoma DNA and peptides derived from purified, radiolabeled T antigene, separated by two-dimensional electrophoresis and chromatography. We compared the peptides, predicted from the nucleotide sequence of the DNA, with those derived from the purified T antigens. We also compared chemically synthesized peptides, predicted from the DNA sequence, with observed peptides. The results show that the three polyoma T antigens are encoded in overlapping regions of the viral DNA, translated, in part, in two different reading frames. © 1979 Information Retrieval Limited.