Epidermal growth factor (EGF) is a peptide which stimulates cell mitotic activity and differentiation, has a cytoprotective effect on the gastroduodenal mucosa, and inhibits gastric acid secretion. The immunohistochemical localization of EGF in the Brunner's glands and the submandibular glands is well documented. The localization of EGF in other tissues is still unclarified. In the present study, the immunohistochemical localization of EGF in tissues from rat, man and a 20 week human fetus were investigated. In man and rat, immunoreaction was found in the submandibular glands, the serous glands of the nasal cavity, Brunner's glands of the duodenum, the Paneth cells of the small intestine, and the tubular cells of the kidney. In the fetus EGF was found in the kidney and in the intestinal Paneth cells. Antisera raised against rat submandibular EGF did not recognize EGF in human tissues, whereas antisera against human urinary EGF worked in rat as well as man. EGF was found only in cells with an exocrine function.