A targeting vector was used to introduce a histidine to aspartic acid substitution mutation at codon 67 (p.H67D). A single loxP site remained in intron 3 after the cre-mediated excision of a loxP site flanked neomycin resistance gene cassette from the germline. The mutation was designed to recapitulate the human mutation, p.H63D, observed in many patients with hereditary hemochromatosis (HH). Northern blot and RT-PCR analyses indicated the expected mutant transcript is expressed at levels similar to that of wild-type.