Possible mechanisms of transmission of Pseudomonas cepacia in hospitalized patients with cystic fibrosis were examined. Twelve patients were colonized with P. cepacia prior to admission (group 1), and 15 patients were not (group 2). Daily contact occurred between both groups. Sputum cultures were obtained from all patients at admission and discharge, and 3 and 6 months after discharge in group 2 patients. Environmental cultures included cough plates, settle plates, spirometry tubing, stethoscopes, sinks, wall outlets, and hands of patients, physicians, nurses, and respiratory therapists. Specimens were plated on a P. cepacia-selective medium. All group 1 patients remained colonized with P. cepacia at discharge. None of the group 2 patients acquired P. cepacia during hospitalization or follow-up. P. cepacia was recovered from three of 151 environmental cultures; two of these were presumably patient related. P. cepacia contamination of pulmonary function equipment, wall outlets, hands, and stethoscopes was not documented. We conclude that transient aerosol environmental contamination is uncommon and restricted to the immediate patient environment.