Studies were conducted on three strains of Pseudomonas cepacia isolated and maintained in distilled water and on a laboratory-subcultured strain transferred to distilled water. Optimum growth rates and maximum population yields of the four strains in distilled water were obtained at 37 C, although high population levels (10(6)-10(7)/ml) were reached and maintained over extended incubation periods at temperatures from 18 C to 42 C. Two strains were able to grow in distilled water at temperatures ranging from 12 C to 48 C and to survive 48 h and 21 days at 50 C and 10 C, respectively. Cells from distilled water cultures inoculated into Trypticase soy broth showed an immediate two- to three-log drop at upper and lower temperature limits; survivors were able to initiate logarithmic growth. Results obtained in morphological, biochemical, and antibiotic tests affirmed the strain differences noted in growth studies.