Pseudomonas aeruginosa has emerged as an important pathogen during the past two decades. It causes between 10% and 20% of infections in most hospitals. Pseudomonas infection is especially prevalent among patients with burn wounds, cystic fibrosis, acute leukemia, organ transplants, and intravenous-drug addiction. P. aeruginosa is a common nosocomial contaminant, and epidemics have been traced to many items in the hospital environment. Patients who are hospitalized for extended periods are frequently colonized by this organism and are at increased risk of developing infection. The most serious infections include malignant external otitis, endophthalmitis, endocarditis, meningitis, pneumonia, and septicemia. The likelihood of recovery from pseudomonas infection is related to the severity of the patient's underlying disease process. The introduction of the antipseudomonal aminoglycosides and penicillins has improved substantially the prognosis of these infections. Ticarcillin and carbenicillin have been especially beneficial in neutropenic patients; however, prompt institution of therapy is mandatory for optimal benefit. Many new drugs with antipseudomonal activity, including penicillins, cephalosporins, and other β-lactams, have been introduced in recent years and offer the potential for new approaches to therapy for these infections.