During a two-month period, six patients in an intensive care unit (ICU) were colonized or infected with Pseudomonas paucimobilis, a newly described bacterial species. To our knowledge, the epidemic organism had not been found previously in these units. The bacterium was usually recovered from the sputum of persons receiving ventilatory assistance and represented transient colonization. One patient had a symptomatic urinary tract infection. The outbreak was confined to two of the ICUs. Cultures of respiratory equipment were negative, but P paucimobilis was recovered from the ICU hot water line. Water bottles used for rinsing tracheal suction connecting tubing were found to contain P paucimobilis organisms. This resulted from refilling with tap water. No further cases were found during a 20-month follow-up period, when a uniform tracheal suctioning policy was developed.