SUMMARYThe human stomach has a normal circadian rhythm of intragastric acidity characterized by increasing acidity during the day and peaks in the early hours of the morning. Eating causes a transient decrease of intragastric acidity. Acid appears to be the permissive factor in peptic ulcer disease and to be responsible for symptoms; the patient with duodenal ulcer may secrete too much acid. Pharmacological control of gastric acid secretion will speed ulcer healing. Modern regimens, which typically use a bedtime dose of an H2‐receptor antagonist, produce a pulse of decreased acidity. Intragastric acidity is decreased during the night and early morning, leaving a normal profile of acidity during the day and early evening. Higher or more frequent doses of an antisecretory agent can produce a more profound decrease of 24‐h intragastric acidity. Theoretical problems associated with a sustained or profound decrease of 24‐h intragastric acidity include the threat of enteric infection and infestation, potential bacterial overgrowth with possible N‐nitrosamine formation, and drug‐induced hypergastrinaemia. In light of these potential problems, for the management of simple peptic ulceration, it appears sensible to use the minimum intervention required. Bedtime H2‐receptor blockade is one such regimen. The more potent antisecretory regimens can be used for difficult clinical problems such as the Zollinger–Ellison syndrome, intractable duodenal ulceration, and severe