1. The existing procedures recommended for the detection of carriers of enteric pathogens are reviewed.2. The techniques employed in this work at present were re-examined.3. An investigation of the sera of 67 chronic typhoid carriers and 343 normal persons, suggested that titrations for typhoid Vi, O and H agglutinins are useful screening tests for the detection of typhoid carriers. The examination may be usefully extended to the titration of H agglutinins against paratyphoid B and paratyphoid A, the former as a possible indicator of the carriage ofSalm.paratyphid B, the latter as an indicator of previous inoculation with T.A.B. vaccine.4. Inoculation did not appear to increase the proportion of positive reactions with TVi bacterial suspension, which in uninfected persons was about 1%. In contrast, the proportion of positive reactors with TO suspension rose from 8·8% in uninoculated to 25·3% in inoculated persons, at a serum dilution of 50; and with TH suspension the positive figure rose from 2·7% in uninoculated to 71·4% in inoculated persons at a serum dilution of 25. Inoculation thus impairs the value of TO agglutination and destroys that of TH agglutination as indicators of infection.5. The investigation of 29 chronic carriers showed that a single bacteriological examination of excreta for the presence ofSalm. typhiis not a reliable method of carrier detection. Increasing the number of specimens to three greatly raises the probability of detection.6. The findings are discussed and a revised form of paragraph 5 of the Ministry of Health Memorandum on the safeguards recommended for adoption by water undertakings is suggested.The Working Party is grateful to a number of pathologists for the supply of sera from chronic carriers and we should also like to thank Mr F. J. Flyn of the Central Enteric Reference Laboratory for his great technical help.