A method for measuring the thickness of the mucus gel layer present on the gastric mucosa is described. This method enables minimal handling of the mucosal specimens and thereby minimizes the errors connected with tissue handling. Male Sprague-Dawley rats were used. With the rats under general anesthesia, the stomach was excised and opened along the greater curvature, and full-thickness biopsy specimens from the corpus region were obtained by means of a skin biopsy punch. From these specimens a slice of mucosa, 1 mm thick, was rapidly cut out and put into a specially made glass chamber containing 0.9% NaCl. The chamber was sealed with a cover glass. Mucus gel layer thickness could then be measured in a conventional light microscope operated at a primary magnification of x120. This method was tested on two groups of 10 rats. The animals in the control group were given 1 ml of 0.9% NaCl, and the rats in the experimental group were given 1 ml of sodium salicylate, 75 mg/kg, dissolved in saline. After 15 min the animals were anesthetized and specimens prepared for measuring mucus gel layer thickness. In the control group, the mucus gel layer measured 145 microns, whereas in the experimental group it reached a thickness of 305 microns. The method proved to be easy to use, and the effects of pharmacologic substances on the mucus gel layer in the stomach could be investigated.