The stability of some antispasmodics mixed with antacid was examined, and the effect of combined administration of these two drugs was studied by experimental peptic ulcer. The antispasmodics used seemed not to be decomposed when they were mixed with synthetic aluminum silicate. From the resuls of the assay with mydriasis of mice eyes, is was shown that the antispasmodics by the antacid reduced the abesorption of these drugs from gastroin-tetinal tract, but practically this will not affect their pharmacological activity seriously, because gastric juice will facilitate the dissociation of the drug from antacid. To examine the effects of the drugs on peptic ulcer, Shay rats were used. Ulcer formation on Shay rat's stomach was treated as the duantal response, and ED 50 of some drugs was calculated. By this method it was shown that synergism of antispasmodics with antacid was of the type of potentiation.