A remarkable sudden increase in the incidence and pathogenicity of Aerobacter aerogenes (Bacillus lactis aerogenes) in the genitourinary tract was reported from the Beth Israel Hospital by Wilhelm and Orkin1in 1948 (published in 1949). At that time this organism was found, either in pure form or in association with other organisms, in the urine of 49.2 per cent of 257 consecutive patients admitted to the urologic service. Studies made subsequently by us in 100 consecutive admissions revealed that A. aerogenes was present in the initial urine cultures of 50 per cent of these patients and that the organism was recovered in later cultures in 75 per cent of the patients at some time during their hospital stay. Bacteremia caused by A. aerogenes was proved in 24 patients, 7 of whom died. In one of the fatal cases, suprapubic prostatectomy was complicated by an acute bacterial endocarditis.2At