The 16S rDNA sequences of four strains, i.e. three type strains of Actinobispora and strain 6330T, were determined and compared with those of representatives of the family Pseudonocardiaceae by using two tree-making algorithms. All the validly described species of the genera Actinobispora and Pseudonocardia were consistently recovered as a mixed group in phylogenetic trees, and were distinct from the other genera of the family Pseudonocardiaceae. Strain 6330T formed a distinct phyletic line in the 16S rDNA tree and was most closely associated with the type strain of Actinobispora aurantiaca. The use of specific PCR primers designed for differentiating the genus Pseudonocardia from other genera of the family Pseudonocardiaceae showed that all the Actinobispora species and strain 6330T have the same amplified 640 bp 16S rDNA fragment as members of the genus Pseudonocardia. The DNA-DNA relatedness, chemotaxonomic and phenotypic data also supported classification of these taxa in the genus Pseudonocardia, and distinguished each from the others. On the basis of these observations, it is proposed that the genera Actinobispora and Pseudonocardia be combined in an emended genus Pseudonocardia, and that strain 6330T be classified in the same genus as Pseudonocardia zijingensis sp. nov. The type strain is 6330T (= AS 4.1545T = JCM 11117T).