This prospective, double-blind, placebo-controlled study was undertaken to determine the value of prophylactic oxacillin in dog bites. Adult patients with uninfected full-thickness wounds presenting within 24 hours of injury were considered. Management consisted of cleansing, irrigation, debridement, and closure as indicated; no topical antibiotics were applied. Patients were randomly assigned to receive oxacillin 500 mg QID x 5 days or identically appearing placebo. Home wound care was standardized an patients were observed at least every 2 days. Clinical assessment of infection was confirmed microbiologically. Sixty-three patients were admitted and 46 completed the study. Oxacillin (22) and placebo (24) groups were identical in sex, age, number of wounds per patient, wound location and type, number of open and closed wounds, delay to presentation, length of follow-up observation, medication compliance, and adequacy of patient wound care. Two infections of the hand occurred in patients receiving oxacillin; no infections were seen among placebo-treated patients (P = NS). Prophylactic oxacillin was not associated with improved outcome. We do not advise the use of prophylactic antibiotics in dog bite injuries treated within 24 hours of accident.