Of 30 cases of olecranon and prepatellar bursitis, ten were septic. Fever, tenderness, peribursal cellulitis, and skin involvement over the bursa were more common in the septic cases. A high leukocyte count, low bursal-to-serum glucose ratio, and positive Gram-stained smear of the bursal fluid distinguished septic from nonseptic bursitis. Rheumatoid arthritis and gout may be accompanied by nonseptic bursitis. Septic bursitis may be associated with a sympathetic sterile effusion in a neighboring joint or adjacent fascial space. The duration of antibiotic treatment necessary to sterilize bursal fluid was proportional to the length of time infection had been present. A prospective antibiotic program disclosed an average of 12 days for successful therapy. A bactericidal agent against penicillin-resistant Staphylococcus aureus is the drug of choice.