The M1-selective antimuscarinic drugs pirenzepine and telenzepine moderately reduce gastric acid secretion without inhibiting smooth-muscle activity as much as nonselective antimuscarinics, e.g. atropine and 1-hyoscyamine. They hasten peptic ulcer healing and improve the symptoms of reflux oesophagitis. In combination with H2 receptor antagonists they abolish gastric acid secretion almost completely and can therefore be used in high-risk peptic conditions. Long-term trials have to show whether they can form a medical alternative to parietal cell vagotomy. The effect of M1-selective antimuscarinics on 'nonulcer dyspepsia' is equivocal, but they may possibly be useful in the treatment of spastic constipation.