HUMAN urogastrone (hUG) is a polypeptide prepared from urine and is chemically similar to mouse epidermal growth factor (mEGF) prepared from submandibular salivary glands. Both these substances stimulate fibroblast proliferation in tissue culture systems. hUG and mEGF inhibit gastric acid secretion in experimental animals and hUG produces an identical effect in man. We show here, using immunofluorescent techniques, that hUG is present in the duct cells of human submandibular gland and in Brunner's gland cells in the first part of the duodenum. This work suggests that these polypeptides may have a role in mucosal growth and control of gastrointestinal secretion.