Polyphasic characterization of strain DSM 9128, described as 'Pseudomonas azelaica' by Janota-Bassalik et al. [Acta Microbiol Pol B 3, 143-153 (1971)], and four biochemically similar isolates was performed with the aim of validly publishing the name 'Pseudomonas azelaica'. Based on 16S rRNA gene sequence analysis, DNA-DNA hybridization, fatty acid patterns and extensive biochemical testing, it was concluded that DSM 9128, two further strains and the type strains of Pseudomonas nitroreducens and Pseudomonas multiresinivorans form a highly related cluster. However, DNA-DNA binding did not conclusively resolve whether these strains should be regarded as members of one species. Based on results gained with the above-mentioned methods, two other isolates were assigned to the species Pseudomonas citronellolis, a species very close to P. nitroreducens. Based on genetic and biochemical similarities, it is suggested that Pseudomonas multiresinivorans should be considered as a later heterotypic synonym of Pseudomonas nitroreducens. The species descriptions of P. nitroreducens and P. citronellolis are emended.