The effects of immunoglobulin E (IgE)-mediated reactions on the intestinal epithelium were examined during intestinal anaphylaxis in the rat. Rats sensitized by intraperitoneal injection of egg albumin (EA) plus alum developed high serum titers of IgE anti-EA antibodies after 14 days; sham-treated littermate controls had no anti-EA antibodies. Two isolated loops of jejunum were prepared in vivo in anesthetized rats. The loops were injected with EA in saline or saline alone, and intraluminal contents of each loop were examined after 4 h. Mucosal histamine decreased in sensitized rat intestine exposed to EA. Luminal mucin, measured by radioimmunoassay, was not increased by antigen challenge. In contrast, DNA, protein, and sucrase activities were elevated in contents from the isolated segments exposed to EA in sensitized rats. Histology revealed that periodic acid-Schiff-stained material was contained in goblet cells in sections prepared from these segments after antigen exposure. Cellular debris was present over the tips of the villi. These findings suggest that IgE-mediated reactions in the intestine cause epithelial damage and loss of material from cells other than goblet cells. The results indicate that release of goblet cell mucus is not a feature of intestinal anaphylaxis.