The activity of alpha- and beta-mannosidase (alpha-MAN and beta-MAN) in seminal plasma, spermatozoa and homogenates of reproductive organs has been determined in the drake. The highest specific activities of the examined mannosidases were found in epididymides. The activities of both enzymes decreased significantly during the postbreeding resting season compared to the breeding season. Elution profiles of multiple forms of mannosidases from particular organs were obtained and characterized. It was found that alpha- and beta-mannosidases in the genital tract of the drake are similar to the enzymes described in other species of domestic fowl. The presence of highly active mannosidases in reproductive tissues and a decline of the mannosidase activities during the postbreeding season strongly suggests that the enzymes take part in reproductive processes of birds.