We have isolated a 3.3-kb DNA containing the two exons and a 2.6-kb intron of the human CPX2 gene. This gene encodes the intestinal isoenzyme of glutathione peroxidase, GSHPx-GI. Consistent signals were detected at 14q24.1 when this DNA was used as a probe for fluorescence in situ hybridization on metaphase chromosomes. Based on either single-stranded conformation polymorphism or sequencing analysis, two sites containing DNA polymorphism were found in the intron: the 5' end had a single A/T alteration, and the 3' end had a microsatellite of TC repeats.