Summary: A combined physical and genetic map of Pseudomonas aeruginosa PAO was constructed by pulsed-field gel electrophoresis and Southern hybridization using cosmid clones from a genomic library carrying known genes. A total of 37 Spel restriction fragments have been mapped on the 5862 kb genome, and fragment contiguity demonstrated by hybridization with clones from a Spel junction fragment library and fragments obtained by partial Spel digestion, both derived from the P. aeruginosa PAO chromosome.