A pair of primers homologous to the nolXWBTUV locus generated a 260 bp fragment by PCR only in the presence of Sinorhizobium fredii template DNA of different quality. This resulted in a fast and accurate method for the identification of S. fredii either from pure DNA, whole bacterial cells or nodule extracts. By means of two PCR fragments, one specific for S. fredii (260-bp) and the other specific for Bradyrhizobium japonicum (RSalpha), we found that S. fredii strain SMH12 and B. japonicum E109 were equally efficient at developing nodules on soybean plants grown under controlled environmental conditions.