During a recent investigation on the carrier problem as it occurs in diphtheria, which was carried out (under the auspices of the Scientific Advisory Committee of the Metropolitan Asylums Board) at the Northern Group Laboratory, North-Eastern Hospital, one of the first subjects considered was that of the bacterial flora of the carriers under examination, and of an adequate series of controls. It was suggested that possibly the flora of the carriers might differ (apart altogether from the presence of the Klebs-Loeffler bacillus) from that found in non-carrier persons of the same age. It was thought that some pathogenic organism might be found to be constantly present in the nose or throat flora of carriers and not in controls, and that this might be exerting an influence on the Klebs-Loeffler bacillus by allowing it to survive in the infected region for prolonged periods. If such were the case it was hoped that an elimination of the organism or organisms concerned would go a long way towards clearing up the carrier condition.