Tests performed according to the Kirby-Bauer method with disks containing streptomycin (300μg), gentamicin (120 μg) and tobramycin (120μg), can be used to identify enterococcal strains which are unusually resistant to one or more of the three drugs. These strains are unlikely to be susceptible to synergistic inhibition by the combination of a penicillin and the aminoglycosides to which they are highly resistant.