Gas liquid-chromatography was used in order to characterize the volatile fatty acids produced in culture supernatants by 632 Pseudomonas strains. Statistical analysis of these results allowed testing of the discriminatory power of this analytical methodology (factor analysis) to point out the presence of subgroups (clustering according to the variance) and to show the relationship between species and subspecies (three-dimensional plot). Fourteen Pseudomonas species could be accurately characterized by this methodology; the classification of Pseudomonas build up, on the basis of qualitative and quantitative aspects of their volatile fatty acids production, agrees with the current classification based on rRNA/DNA homology complexes.