A short-term double-blind study has been conducted to evaluate the clinical efficacy of diltiazem in 18 patients with irritable bowel syndrome, divided into two groups: group A, on the sequence placebo-diltiazem-placebo for three weeks. Group B, diltiazem-placebo-diltiazem for an identical period. The substance was administered in three daily doses of 60 mg prior to meals. Clinical manifestations and the general condition were evaluated after each period of three weeks following a pre-established score. Globally, it has been impossible to demonstrate the superiority of diltiazem over the placebo, but there seems to exist a trend to the improvement of diarrhoea and abdominal pain. It will be necessary to make an additional study to delineate the efficacy of this drug in the irritable bowel syndrome.