Through a controlled vaccination study with artificial challenge, the present study was designed to evaluate the protective value of formalin, saponin or binary ethyleneimine inactivated Mycoplasma gallisepticum adjuvanted bacterins, in comparison with the efficacy of the live Mycoplasma gallisepticum "F" strain vaccine. Protective values of tested vaccines were compared by measuring antibody titers in sera of chicken at different intervals post vaccination by enzyme linked immunosorbent assay (ELISA), serum plate agglutination test and by scoring of sinus lesions after challenge with the virulent Mycoplasma gallisepticum "R" strain. The highest antibodies titer (P < 0.01) were recorded in the group of chicken vaccinated with the binary ethyleneimine inactivated vaccine that peaked at two weeks post-vaccination and remained elevated till the end of experiment. Meanwhile, the saponin-inactivated Mycoplasma gallisepticum elicited a comparable humoral immune response with that elicited by the binary ethyleneimine vaccine, the least immunizing effect was observed in the formalin inactivated Mycoplasma gallisepticum bacterins immunized chicken. Challenge of vaccinated birds was performed by intrasinus injection of 1 x 10(9) colony forming units of virulent "R" strain of Mycoplasma gallisepticum. While, similar degree of protection was afforded by binary ethyleneimine and saponin inactivated bacterins as well as the live "F" strain vaccine, the formalin-inactivated Mycoplasma gallisepticum bacterin showed lesser degree of protection. The obtained results indicated that inactivated bacterins could elicit a protective response in chicken, thus offering a new trend in the control and eradication of Mycoplasma gallisepticum from chicken flocks.