Phylogenetic analyses of 16S rRNA gene sequences by distance matrix and parsimony methods indicated that the currently known species of the genus Sphingomonas can be divided into four clusters. Some chemotaxonomic and phenotypic differences were noted among these clusters. Three new genera, Sphingobium, Novosphingobium and Sphingopyxis, are proposed in addition to the genus Sphingomonas sensu stricto. The genus Sphingobium is proposed to accommodate Sphingomonas chlorophenolica, Sphingomonas herbicidovorans and Sphingomonas yanoikuyae. The genus Novosphingobium is proposed for Sphingomonas aromaticivorans, Sphingomonas capsulata, Sphingomonas rosa, Sphingomonas stygia, Sphingomonas subarctica and Sphingomonas subterranea. Sphingomonas macrogoltabidus and Sphingomonas terrae are reclassified in the genus Sphingopyxis. The type species of Sphingobium, Novosphingobium and Sphingopyxis are Sphingobium yanoikuyae, Novosphingobium capsulatum and Sphingopyxis macrogoltabida, respectively.