Figure 3. A surgical specimen from an AIDS patient who had a small-bowel resection for a perforated cytomegalovirus ulcer. Special stains for cytomegalovirus (CMV) are shown. Left. Cytomegalic cells were rare in the glandular epithelium of this patient, but they were easily identified by this in-situ DNA hybridization that stains the enlarged nucleus purple (original magnification, x 200). Center. In the same patient, many smooth muscle cells and fibroblasts stain purple, indicating the presence of CMV DNA (original magnification, x 400). Right. Immunoperoxidase stain (using a monoclonal antibody against a CMV antigen) that stains infected cells brownish-red (original magnification, x 400).