1. The effects of epidermal growth factor on the synthesis and secretion by human gastric mucosa of radiolabelled mucus glycoprotein have been studied in organ culture. 2. Addition of epidermal growth factor at a concentration of 5 or 10 ng/ml increased the synthesis of glycoprotein from 84 +/- 16.2 d.p.m./micrograms of protein to 132 +/- 19.5 and 156 +/- 20.2 d.p.m./micrograms of protein, respectively. The same doses increased secretion from 73.75 +/- 17 d.p.m./micrograms of protein to 114.0 +/- 26.4 and 141.5 +/- 31.4 d.p.m./micrograms of protein (P less than 0.001). 3. As glycoproteins are the main constituent of the mucus defence barrier, epidermal growth factor-stimulated mucus production may contribute to gastric cytoprotection.