Intestinal contents obtained at necropsy from 100 patients, 99 of whom died while in hospital, were examined for Ps. aeruginosa. The contents were taken from four sites; the organism was isolated from all sites in eight patients. The over-all carriage rate was 36 per cent., but the rate was increased to 43-2 per cent, if oral antibiotics had been administered, and to 52-6 per cent, if gastro-intestinal surgery had been performed.