Eight carriers of intestinal pathogens (5 Salm. typhi-murium, 2 Sh. sonnei, 1 E. coli 026) were given their own coliforms, rendered drug-resistant in vitro to neomycin or paromomycin, together with one of these drugs. In seven cases, the drug-resistant coliform flora established itself, while the natural coliform flora and the pathogen were suppressed. In four cases only (2 Sh. sonnei, 2 Salm. typhi-murium) the pathogen was eliminated in the course of this procedure.