Patients with chronic granulomatous disease (CGD) have recurrent infections with catalase-producing organisms, particularly staphylococci, that survive within their leukocytes. To be most effective, antibiotics used to treat infections in CGD patients may need to kill both intracellular and extracellular organisms. We studied the ability of certain antibiotics to penetrate normal and CGD neutrophils and to kill intracellular staphylococci. Trimethoprim and clindamycin were concentrated in normal and in CGD neutrophils; maximum cellular-to-extracellular concentration ratios of clindamycin and of trimethoprim were approximately 30 and approximately 4, respectively. In contrast, penicillin was excluded from normal neutrophils. Clindamycin, trimethoprim/sulfamethoxazole, rifampin, and trimethoprim/rifampin significantly reduced the number of viable intracellular staphylococci in normal and CGD neutrophils. After 24 h of incubation in the presence of these antibiotics, the number of viable intracellular staphylococci in normal and CGD neutrophils was similar. In contrast, dicloxacillin, gentamicin, and cephalothin had no significant effect on the number of intracellular staphylococci in normal or CGD neutrophils.