A group of four diverse rhizobial isolates and two soil isolates that are highly related to Ensifer adhaerens were characterized by a polyphasic approach. On the basis of DNA-DNA hybridizations and phenotypic features, these strains cannot be distinguished clearly form Ensifer adhaerens, a soil bacterium that was described in 1982, mainly on the basis of phenotypic characteristics. Phylogenetically, Ensifer and Sinorhizobium form a single group in the 16S rDNA dendrogram of the alpha-Proteobacteria, as well as in an analysis of partial recA gene sequences. They may therefore be regarded as a single genus. Because Sinorhizobium was proposed in 1988, according to the Bacteriological Code (1990 Revision) the older name, Ensifer, has priority. However, there are several reasons why a change from Sinorhizobium to Ensifer may not be the best solution and making an exception to Rule 38 may be more appropriate. We therefore propose the species Sinorhizobium adhaerens comb. nov. and put forward a Request for an Opinion to the Judicial Commission regarding the conservation of Sinorhizobium adhaerens over Ensifer adhaerens.