The taxonomy of the "diminuta" group is discussed. The method of numerical taxonomy was used to characterize 135 strains of 10 species belonging to Pseudomonas, Gluconobacter and Acetobacter in terms of sixty phenotypical features. The similarity coefficients of the strains were calculated with computers. According to the data of numerical analysis, the species P. diminuta and P. vesiculare represent a single phenon different from Pseudomonas, Gluconobacter and Acetobacter species.