Summary Over a 30-day period, Acinetobacter calcoaceticus var. antiratus was the responsible pathogen for hospital-acquired pneumonia in 10 patients, and resulted in the colonization of the upper respiratory tract in an additional 9 patients. Wright respirometers contaminated by this organism were shown to be the common source for the outbreak as indicated by the recovery of a single serotype (8J), the inability to recover Acinetobacter from any other environmental source, and the demonstration that moisturized Wright respirometers are capable of "aerosolizing" fluids containing Acinetobacter.