Duodenal ulcers were induced in ovariectomized, intact and old mice using cysteamine hydrochloride. Under these experimental conditions ovariectomy and old age strikingly increased sensitivity to ulcer induction while estrogen administration showed a decrease in sensitivity to ulcer induction. Nevertheless, the administration of estrogen in old mice showed no effects in either intact or overiectomized mice. This change in ulcer sensitivity reflected from histological, histochemical and biochemical studies. The histological study was performed by using haematoxylin-eosin and haematoxyline staining technique. The histochemistry of the duodenal region was studied by using periodic acid Schiff reaction (PAS) for glycoproteins. The biochemical study was performed to study various constituents of glycoproteins like hexose, fucose, sialic acid and the protein. The result showed that ulcer severity was more in overiectomized cysteamine treated mice and old mice treated with cysteamine. The histological studies showed that ovariectomy decreased or did not show any change in the ulcer sensitivity considering cryptus Lieburkuhn and Brunner's glands. The same result reflected by differential intensity in the staining property of the Brunner's gland. The biochemical study showed that the glycoprotein contents were reduced many times in overiectomized cysteamine treated mice and their reversal in estrogen administered ovariectomized cysteamine injected mice. These findings prove that estrogen protects the duodenal ulcer from cysteamine administration.