There have been no comprehensive microbiologic studies of the frequency of respiratory colonization with nonfermentative gram-negative rods (NFGNR) other than Pseudomonas aeruginosa in patients with cystic fibrosis (CF). Records of bacteria isolated from throats and sputa of CF patients of the Yale-New Haven Hospital CF Clinic from 1975-1979 were reviewed in order to determine the incidence of these species. Thirty-one strains were recovered. Twenty patients from the CF Clinic (with an average census of 170 patients) yielded at least one isolate of non-P. aeruginosa NFGNR, and eight of them showed more than one species on at least one occasion. Two patients also carried P. aeruginosa and ten carried Staphylococcus aureus on at least one occasion. Using a standardized method of clinical scoring, our patients had a course not unlike our general CF population.