Three types of liquid and tablet antacids have been studied in vitro and in vivo: aluminium hydroxide, aluminium hydroxide‐magnesium carbonate and hydrotalcite. The effects on gastric pH of antacid suspensions and antacid chewing tablets having identical active ingredients have been studied in 36 volunteers, the sequence of both forms of administration being randomized. Gastric acid secretion was continuously stimulated during the experiment by a pentagastrin infusion. Antacid chewing tablets gave inferior results when compared with the same antacid in liquid. Antacid suspensions are therefore preferred in the treatment of acid‐peptic disease.