We investigated the ability of a recently developed genomic fingerprinting technique, named AFLP, to differentiate the 14 currently defined DNA hybridization groups (HGs) in the genus Aeromonas. We also determined the taxonomic positions of the phenospecies Aeromonas allosaccharophila, Aeromonas encheleia, Aeromonas enteropelogenes, and Aeromonas ichthiosmia, which have not been assigned to HGs yet. A total of 98 Aeromonas type and reference strains were included in this study. For the AFLP analysis, the total genomic DNA of each strain was digested with restriction endonucleases ApaI and TaqI. Subsequently, restriction fragments were selectively amplified under high-stringency PCR conditions. The amplification products were electrophoretically separated on a polyacrylamide gel and visualized by autoradiography. Following high-resolution densitometric scanning of the resulting band patterns, AFLP data were further processed for a computer-assisted comparison. A numerical analysis of the digitized fingerprints revealed 13 AFLP clusters which, in general, clearly supported the current Aeromonas taxonomy derived from DNA homology data. In addition, our results indicated that there is significant genotypic heterogeneity in Aeromonas eucrenophila (HG6), which may lead to a further subdivision of this species. A. allosaccharophila and A. encheleia did not represent a separate AFLP cluster but were found to be genotypically related to HG8/10 and HG6, respectively. In addition, the results of the AFLP analysis also confirmed the phylogenetic findings that A. enteropelogenes and A. ichthiosmia are in fact identical to Aeromonas trota (HG13) and Aeromonas veronii (HG8/10), respectively. The results of this study clearly show that the AFLP technique is a valuable new high-resolution genotypic tool for classification of Aeromonas species and also emphasize that this powerful DNA fingerprinting method is important for bacterial taxonomy in general.