The genus Acinetobacter is subdivided into genospecies on the basis of DNA relatedness of strains. Phenotypic tests are insufficient to identify the genospecies to which an isolate belongs. The effectiveness of two previously described PCR-based methods for genospeciating Acinetobacter spp. was compared using a group of 32 well-characterised strains representing six genospecies. Amplified ribosomal DNA restriction analysis (ARDRA) correctly identified all 32 strains. Using restriction fragment length polymorphism (RFLP) of recA PCR amplimers, only six of the 32 strains were correctly identified. Heterogeneity in the recA gene sequence was demonstrated within five of the genospecies. ARDRA proved to be a reliable method whereas analysis of recA RFLP profiles did not enable the genospecies of most of the isolates of Acinetobacter spp. to be determined. z