The location of [125I]iodotyrosyl gastrin-releasing peptide-binding sites in the rat fundic mucosa was studied. Peptide specificity was demonstrated by competitive binding studies using the addition of a large amount of cold gastrin-releasing peptide or substance P. Autoradiography of the stomach tissue was carried out by freeze-drying, embedding in Epon, wet-sectioning with ethylene glycol, and dry-mounting the emulsion film by the wire-loop method to prevent loss of the labeled substance. Specific binding sites of gastrin-releasing peptide were found on D cells, surface mucus cells, and parietal cells, whereas few binding sites were seen on the chief or mucus neck cells.