The effect of a new calcium antagonist, nifedipine, which has a spasmolytic activity on smooth muscle cells, was studied on the esophageal function of 20 patients with achalasia of mild and moderate degree. The study was carried out by using constantly perfused catheters and recording the pressure variations at the lower esophageal sphincter, before and after sublingual administration of 10-20 mg of nifedipine. The drug significantly decreased the lower esophageal sphincter pressure for more than 1 h. A clinical trial was also carried out by assessing the improvement of symptoms in achalasia patients taking sublingually a dose of 10-20 mg of nifedipine before each meal. After 6-18 mo of nifedipine therapy these patients underwent a placebo treatment, whereas an additional group of 9 achalasia patients was treated first with placebo followed by nifedipine. The nifedipine treatment gave excellent or good results in a large majority of patients of both groups. The moderate results were only 5 and the poor responses only 3. The clinical improvement induced by nifedipine was statistically significant when compared, not only with the pretreatment clinical state, but also with the results of the placebo treatment. No tachyphylaxis and few side effects were seen either during the manometric recordings or the longest periods of therapy. This study suggests that nifedipine may be advantageously used in the medical treatment of achalasia of mild or moderate degree.