Exposure to Mycoplasma gallisepticum induces severe lymphoproliferative lesions in multiple sites along the respiratory tract in chickens and turkeys. These immunopathological responses have been well defined in chickens, but have not been studied closely in turkeys. The aim of the studies described here was to examine the immune responses of turkeys after vaccination and infection with M. gallisepticum. In a strain comparison study, the mean log10 antibody titre of birds exposed to an aerosol culture of M. gallisepticum strain Ap3AS was found to be significantly higher at day 14 than that of birds exposed to strain 100809/31. In a dose response study, there was a significant difference in the mean log10 antibody titre between birds exposed to mycoplasma broth and birds exposed to the highest dose of strain Ap3AS at day 7 after exposure (P < 0.5). Immunohistochemical analysis of the tracheal mucosa and the air sacs revealed similar patterns of distribution of CD4+ and CD8+ lymphocytes to those seen in the tracheal mucosa of chickens, implicating these cell types in the pathogenesis of respiratory mycoplasmosis in turkeys. Turkeys that had been vaccinated with M. gallisepticum GapA+ ts-11 had significantly higher antibody titres than unvaccinated birds at both 7 and 14 days after challenge with strain Ap3AS. This study adds to a growing body of evidence that M. gallisepticum infections can induce similar immune responses in different avian species, and also showed that the GapA+ ts-11 vaccine provides effective protection than the current ts-11 vaccine, possibly through inducing superior levels of mucosal immunity.