Comparison of polypeptide patterns of five mycoplasma strains isolated from tissue cultures (M. orale, M. arginini, M. salivarium, M. hyorhinis and A. laidlawii using sodium dodecyl sulphat polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis was carried out. The SDS-PAGE protein profiles of mycoplasmas isolated from tissue cultures showed two common antigens at 45 and 49 kilodaltons (P45 and P49). The immunoreactivity in Western blots of the Strains using M. arginini and M. hyorhinis anti-rabbit sera proved that P45 was found to be more immunogenic than p49. Triton X-114 phase partitioning has revealed the hydrophilic nature of P45 and P49. Antisera raised to electroeluted P45 and P49 reacted specifically with these proteins when assessed on immunoblots of the examined five mycoplasma strains.