Whole-cell fatty acid profiles of 36 strains of Moraxella and its related bacteria, and 13 strainsof Legionella pneumophila were obtained by capillary gas chromatography (GC). Some component peaksin these profiles were analyzed by gas chromatography-mass spectrometry (GC-MS). Hierarchical clus-tering analysis of these bacterial fatty acid patterns was done with a microcomputer. Results showedthat these were some obvious differences between the two new species of Moraxella isolated in China,i.e. M. amylolytica and M. nanchang, and the currently established reference strains of this genus. Themajor fatty acids of these two new species were the isomers of pentadecanoic (C_(15:0)) acids. Theprofiles of L. pneumophila NJ 8331 and LDB 4_a recently isolated in China were essentially similar tothose of international reference strains type 1-8 (CDC, USA), which contained mainly 16-carbon (C_(16))acids, whereas another isolate LDB 4b was obviously dissimilar. The results of this method of discrim-ination and of t Whole-cell fatty acid profiles of 36 strains of Moraxella and its related bacteria, and 13 strains of Legionella pneumophila were obtained by capillary gas chromatography (GC). Some component peaks in these profiles were analyzed by gas chromatography-mass spectrometry (GC-MS). Hierarchical clustering analysis of these bacterial fatty acid patterns was done with a microcomputer. Results showed these were some obvious differences between the two new species of Moraxella isolated in China, ie M. amylolytica and M. nanchang, and the currently established reference strain of this genus. Themajor fatty acids of these two new species were the isomers of pentadecanoic (C_ (15: 0)) acids. Theprofiles of L. pneumophila NJ 8331 and LDB 4_a recently isolated in China were similar 1-8 (CDC, USA), which contained mainly 16-carbon (C_ (16)) acids, whereas another isolate LDB 4b was obviously dissimilar. The results of this method of discrimination m-ination and of t