Thirteen strains of mycobacteria isolated from deer and various species of wild birds were analysed by gas chromatography (GG) for cellular fatty acids and by thin-layer chromatography (TLG) for polar lipids. These strains were compared to reference strains of Mycobacterium avium, M. para tuberculosis and M. mal-moense. All the examined strains exhibited a generally similar fatty acid pattern characterized by relatively large amounts of hexadenca-noate (16:0), octadecenoate (18:1), octadecanoate (18:0) and 10-me-thyl-octadecanoate (tuberculostearic acid, 10-Me-18:0). Several additional acids were also generally present but in smaller amounts. By means of small but distinct differences in fatty acid composition, the wild animal isolates could be distinguished from both M. paratuber-culosis and M. malmoense but not from M. avium. The TLG polar lipid patterns on the other hand separated the wild animal isolates into 2 distinct groups of complex and simple polar lipid composition which corresponded to the morphologically smooth and rough types, respectively. The complex patterns of the smooth strains were comparable to those of the M. avium serovars whereas both the rough wild animal isolates and all the M. paratuber-culosis strains showed a simple pattern of polar lipids. Both fatty acid profiles and TLG polar lipid patterns support allocation of the wild animal isolates to the MAIS complex. Moreover, the 2 chemical techniques, particularly the GC procedure, are very useful for a more rapid and precise identification of the slow-growing wild animal mycobacterial isolates which have hitherto been characterized on basis of vague criteria.