Chronic exposure to high concentrations of hexavalent chromium [Cr(VI)] in drinking water induces duodenal tumors in B6C3F1 mice. Available data indicate that these tumors are the result of chronic villus epithelial cell damage followed by crypt proliferation, as opposed to direct effects on stem cells within the crypt compartment. To assess the health of the crypt compartment following Cr(VI) exposure, an OECD and GLP compliant in vivo duodenal micronucleus study was conducted in B6C3F1 mice. Specifically, mice (n=5 per dose group) were exposed to 0, 1.4, 21, or 180 mg/L Cr(VI) in drinking water for 7 days, and their duodena were removed, trimmed using the “Swiss roll” technique, processed routinely for formalin fixation and paraffin embedding (FFPE), stained with Feulgen’s stain, and sectioned to 5-mm. Using image analysis software, micronuclei were counted in 15 or more crypts per animal, resulting in analysis of 3,000 to 5,000 crypt epithelial cells per treatment group. Consistent with increased proliferation, the number of enterocytes per crypt increased 1.7-fold from 40.0 ± 3.5 to 67.1 ± 5.5 in the high dose group; however, micronuclei were not elevated in any of the mice exposed to Cr(VI). Consistent with the lack of micronuclei, X-ray fluorescence microscopy conducted on FFPE 20-mm Swiss roll duodenal sections revealed little to no Cr fluorescence in control mice, whereas Cr fluorescence was localized to the duodenal villi of mice exposed to 180 mg/L Cr(VI). In contrast, Ca fluorescence was detected throughout the duodenal sections. In addition to these data, we also describe results from g-H2AX immunostaining in the duodenum. Unlike transverse sections that limit analysis to a single point along the duodenum, Swiss roll sections allow for greater longitudinal coverage along the intestine. Together, the data herein support that Cr(VI) does not adversely effect the health of the crypt compartment along the length of the duodenum of B6C3F1 mice.