Immunohistological staining of mitotic cells in the ileum of GPX-DKO mice with disrupted both Gpx1 and Gpx2 genes. Mice were injected with bromodeoxyuridine (BrdU) 2 h before euthanasia. Extended from the crypt epithelium, the mitotic cells, which incorporated BrdU for DNA synthesis, were detected with an anti-BrdU antibody. The dark brown staining was produced by streptavidin-peroxidase, which binds to the biotin-conjugated 2^nd antibody. The cells were counterstained with hematoxylin. For details, see the article by Chu et al. on p. 962 of this issue.