There is recent enhanced interest in the potential of medication to produce serious toxicity, and the television media have focused on the serious side effects and drug-drug interactions caused by antibiotics. In fact, a recent hospital study noted that drug-related toxicity was one of the most common causes of death for hospitalized patients. Antibiotic-induced adverse events contribute to host injury diagnostic confusion and excessive medical costs. In addition, however, a "spin-off'' of antibiotic-induced adverse events is the emergence and dissemination of drug-resistant organisms. This chapter will describe the adverse events and drug-drug interactions produced by those antibiotics that are most commonly prescribed to patients to prevent or treat respiratory tract infections. An effort will also be made to focus on those unique settings (the patient with renal insufficiency, the patient receiving immunosuppressive medication, the pregnant patient, the elderly patient, and the HIV-infected patient who is a candidate for primary or secondary prophylaxis for Pneumocystis carinii) that require a knowledge of antibiotic-induced adverse events.