To generate the antibodies to the transforming protein (p28sis) of simian sarcoma virus (SSV), the rabbits were immunized with peptides, corresponding to 200-206 and 201-210 sequences of p28sis, conjugated with protein carriers by different ways. The synthesis of peptides was carried out by the classical techniques in solution by using the benzyl type side protecting groups. Antibody titres against peptides were determined by ELISA and protein specificity by radioimmunoprecipitation and immunoblotting. It was shown that the antibodies to 201-210 peptide recognize p28sis and its dimer p56sis in marmoset and rat cells transformed by simian sarcoma virus.