Sixteen infections caused by Staphylococcus aureus and six infections caused by S albus were treated with gentamicin sulfate. The antibiotic was effective in eradicating the S aureus infections in all but two patients. All six infections due to S albus were cured. No significant toxic effects were detected and superinfection developed in only one patient. The clinical efficacy of gentamicin correlated with its in vitro activity as determined by tube-dilution and disk-diffusion assays. All isolates of S aureus were inhibited by 3.1μg/ml or less of gentamicin; all isolates of S albus were inhibited by 0.78μg/ml or less of gentamicin. The bactericidal concentrations of gentamicin were never greater than twice the inhibitory concentrations.