Genetic mapping of the genes (puu) that encode the enzymes catalysing degradation of purines in Pseudomonas aeruginosa strain PAO has been carried out. Mutants that are deficient in adenine deaminase (puuA), guanine deaminase (puuB), xanthine dehydrogenase (puuC), uricase (puuD), allantoinase (puuE), and/or allantoicase (puuF) were isolated and used for the genetic study. Conjugation by FP5 factor and generalized transduction by phage G101 gave the following map locations of these six genes on the chromosome: hisI--puuB--hisII; trpA,B--puuA--ilv202; met9011--catA1--tyu--nar9011--(puuC, puuD, puuE)--puuF. A close linkage among the puuC, puuD and puuE was demonstrated by the transduction.