A phenanthrene-mineralizing Pseudomonas sp., designated UG14, was isolated from creosote-contaminated soil. It contained two plasmids, of approximately 77 kb and 76 kb, the smaller of which contained DNA sequences that hybridized with probes specific for ndoB and xylE, genes involved in catabolism of aromatic hydrocarbons. At initial phenanthrene concentrations of 10, 50, 200 and 1000 mg/l broth, 27%, 19%, 7.7% and 3.3%, respectively, of the [9-(14)C]phenanthrene was recovered as (14)CO2 after 36 days' incubation at 30°C. Most (14)C-label was converted to a water-soluble metabolite tentatively identified as 1-hydroxy-2-naphthoic acid. Rhamnolipid biosurfactants produced by P. aeruginosa UG2 enhanced mineralization of 50 mg phenanthrene/l by Pseudomonas sp. UG14. With the biosurfactant at 0, 25 and 250 mg rhamnose equivalents/l, 6.5%, 8.2% and 9.8%, respectively, of the phenanthrene was mineralized after 35 days.