A total of 71 Aeromonas strains was identified with established genomic species by DNA-DNA hybridization. The strains were isolated from diarrhoeal stools, dead and live fish, drinking, lake, river and sea water, municipal sewage and aluminium rolling emulsion. The strains were allocated to seven hybridization groups (HGs) but the majority belonged to HG 4 (42%), HG 8/10 (30%) and HG 3 (18%). All strains were examined by 136 phenotypic tests. Useful phenotypic characters for separation of Aeromonas HG 1-3 genospecies were: utilization of DL-lactate, urocanic acid and growth at 40.5 degrees C. Few phenotypic differences were detected between strains of HG 4, HG 5 and HG 6. Most isolates of the Aer. veronii biotype sobria (HG 8) showed a characteristic biochemical profile: positive V.P. (Voges-Proskauer) reaction, oxidation of gluconate, production of gas from glucose, susceptibility to cephalotin, no hydrolysis of elastin, arbutin and aesculin, and no acid production from L-arabinose, arbutin and salicin.