Gentamicin sulfate is frequently included in the initial treatment of suspected bacterial keratitis. We present the gentamicin susceptibility test results for coagulasenegative staphylococci and Staphylococcus aureus isolated from corneal ulcers in nine patients. All were resistant to gentamicin by standard disk diffusion techniques. The minimum inhibitory concentrations were very high, some exceeding the concentration normally achieved by frequent topical application of antibiotics. Clinicians should be aware that strains of staphylococci extremely resistant to gentamicin may cause keratitis. An antibiotic with broad activity against Gram-positive organisms, such as a cephalosporin or vancomycin, should be included as part of the initial therapy for corneal ulcers that might be caused by staphylococci.