The effects of the anti-acid secretory agents, cimetidine (N-cyano-N'-methyl-N"-(2-([(5-methyl-1H-imidazol-4-yl)methyl]thio)ethyl) guanidine), ranitidine (N-(2-(((-5-[(dimethylamino)methyl]-2-furanyl)methyl)thio)ethyl)-N'-meth yl- 2-nitro-1,1-ethene-diamine), roxatidine (2-acetoxy-N-(3-[m-(1-piperidinylmethyl)phenoxy]-propyl) acetamide hydrochloride), FRG-8813 (2-(furfurylsulfinyl)-N-(4-[4-(piperidinomethyl)-2-pyridyl]o xy-(z)-2- butenyl)acetamide), omeprazole (5-methoxy-2-([(4-methoxy-3,5-dimethylpyridinyl)methyl]sulfinyl)- 1H-benzimidazole), and NC-1300-O-3 (2-([2-(isobutylmethylamino)benzyl]sulfinyl)-1H- benzimidazole), on mucin biosynthesis were studied in rat gastric mucosa by using an organ culture technique. [3H]Glucosamine incorporation was stimulated in the corpus region by the histamine H2 receptor antagonists which have a six-membered aromatic ring, roxatidine and FRG-8813, and the new H+,K(+)-ATPase inhibitor, NC-1300-O-3. Thus, these drugs not only inhibit acid secretion but may also promote gastric mucosal protective actions. The present observations also demonstrate that the determination of mucin biosynthesis may be a useful tool for evaluation of mucosal protective activity.