Twentyfive strains or substrains belonging to the bacterial species Moraxella nonliquefaciens, M. bovis, M. kingii, M. osloensis, M. phenylpyrouvica and M. urethralis (tentative designation) were examined by gas-liquid chromatography (GLC) of whole cell methanolysates. Each strain gave a reproducible chromatogram, usually with no difference between non-fimbriated and fimbriated variants. With a few exceptions, there was no significant difference between the elution profiles of strains belonging to the same species. The study revealed similarities as well as distinct dissimilarities in interspecies comparisons. When compared with M. bovis, the species M. nonliquefaciens and M. phenylpyrouvica showed most similarity, whereas M. kingii revealed the greatest chromatographic deviation. The remaining two species were intermediate in this respect. The results are discussed in relation to taxonomic data previously arrived at by other methods, in particular measurements of nucleic acid homologies and heterologies. Generally, the two groups of results were consistent, and it is concluded that GLC is a valuable tool for evaluation of relationship between species, adding significantly to the reliability of species allocation to genus. GLC appears also applicable for species identification of isolates of moraxellae and similar organisms. However, the sometimes great similarities between closely related species and the occasionally observed (minor) intraspecies variations in elution profile substantiate the need for supplementary methods.