Summary By testing some of the many methods that have been described for the identification of Ps. aeruginosa with a series of typical strains an identification scheme was evolved and subsequently applied in an epidemiological investigation of Ps. aeruginosa respiratory tract infections. Its use led to the rapid identification of typical strains, but even atypical strains were usually identified within 48 hr of their isolation. The scheme has been evolved with the needs of the routine medical diagnostic laboratory in mind.