The genus Acinetobacter comprises Gram-negative coccobacilli that occasionally ap-pear sufficiently round on Gram smears to be confused with Neisseria. On primary isolation, they closely resemble the Enterobacteriaceae in growth pattern and colonial morphology but are distinguished by their failure to ferment carbohydrates or reduce nitrates. As with most of the organisms discussed in later, the isolation of Acinetobacter from clinical material does not define infection, because they appearmost frequently as skin and respiratory colonizers. They are most frequently found as contaminants of almost anything wet, including soaps and some disinfectant solutions. Pneumonia is the most common infection, followed by urinary tract and soft tissue in-fections. Nosocomial respiratory infections have been traced to contaminated inhala-tion therapy equipment, and bacteremia to infected intravenous catheters. Treatment is complicated by frequent resistance to penicillins, cephalosporins, and occasionally aminoglycosides.