Two hundred and seventy five strains of M. avium isolated from cattle (26), pigs (117), sheep (27), hens (102), a wild boar (1), a mink (1) and a sparrow (1) were examined to determine their seriotypes and some biochemical properties. It was found that avian tubercle bacilli of serotype 2 occurred several times more often than M. avium 1. M. avium 3 was isolated sporadically. Some strains of all the three serotypes had atypical biochemical properties for M. avium. Some of them were more active in biochemical tests then typical M . avium, while others were negative in all tests used in the study. A relationship between the serotype and biochemical prioperties was not found.