Homozygous mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis (CF). In the heterozygous state, increased resistance to infectious diseases may maintain mutant CFTR alleles at high levels in selected populations＇. Here we investigate whether typhoid fever could be one such disease. The disease is initiated when Salmonella typhi enters gastrointestinal epithelial cells for submucosal translocation(2). We found that S, typhi but not the related murine pathogen S. typhimurium, uses CFTR for entry into epithelial cells. Cells expressing wild-type CFTR internalized more S. typhi than isogenic cells expressing the most common CFTR mutation, a phenylalanine deleted at residue 508 (Delta 508). Monoclonal antibodies and synthetic peptides containing a sequence corresponding to the first predicted extracellular domain of CFTR inhibited uptake of S. typhi. Heterozygous Delta F508 Cftr mice translocated 86% fewer S. typhi into the gastrointestinal submucosa than wild-type Cftr mice; no translocation occurred in Delta F508 Cftr homozygous mice. The Cftr genotype had no effect on the translocation of S. typhimurium. Immunoelectron microscopy revealed that more CFTR bound to S. typhi in the submucosa of Cftr wild-type mice than in Delta F508 heterozygous mice. We conclude that diminished levels of CFTR in heterozygotes may decrease susceptibility to typhoid fever.