Recently, some Aerococcus-like organisms (ALOs), isolated from urine and blood of elderly patients with urinary tract infection, have been described. In this study ALOs and related taxons were tested for susceptibility by agar diffusion and agar dilution methods to 15 selected antimicrobial agents for diagnostic and taxonomic considerations. ALOs were susceptible to a wide range of antimicrobials including beta-lactams, but resistant to aminoglycosides, sulphonamides, trimethoprim and nalidixic acid. By using tablets containing vancomycin, furazolidone and bacitracin, it was possible to separate ALOs from related taxons. Clustering based on antibiotic susceptibilities showed that there is little similarity between Aerococcus viridans and ALOs.