Erythromycin, first introduced for clinical use 30 years ago, was found to be effective for the treatment of gram-positive bacterial infections. Emergence of resistance and the advent of penicillinase-resistant penicillins limited the use of erythromycin for serious staphylococcal infections; however, erythromycin remains among the drugs of choice for the treatment of acne, infections of the skin and soft tissues, streptococcal pharyngitis, bronchitis, pneumonitis, diphtheria, carriers of pertussis, and, when administered with a sulfonamide, otitis media. Erythromycin is the drug of choice for the empiric treatment of outpatients with pneumonitis. Erythromycin is also the drug of choice for the treatment of Legionella pneumonia and is effective therapy for Chlamydia infections. Other uses of erythromycin include prophylaxis for elective colon operations and treatment of Campylobacter enteritis, genitourinary infections, and some sexually transmitted diseases.