Antacids are drugs of choice in the treatment of reflux esophagitis and peptic ulcer disease, where acid regurgitation may cause dental erosion. Since there are no specific preventive measures or effective treatment for erosions, the present study was made to assess whether the keeping of antacids in the mouth before swallowing would be beneficial with regard to their effect on mouth pH, after acidic challenge. Five healthy subjects formed the test panel. After measuring the acid binding capacity of all the antacid preparations in the Finnish market, the two most effective were selected for testing, one in emulsion form (Novaluzid), the other a tablet (Link). Acid regurgitation was mimicked by consuming a low-pH (3.2) drink immediately before the antacid. Control series were made with the acidic drink only. Both the antacids were found to counteract totally the pH fall caused by the drink, when measured as changes in the tongue surface pH. The Novaluzid preparation was more effective than the Link preparation but the difference was not significant. It may be anticipated that patients suffering from acid regurgitations would benefit if they are counseled to keep their antacids in the mouth for a while before swallowing.