Recently, calcium antagonists have been reported to have a clinically beneficial effect in patients with asthma. Felodipine is a new calcium antagonist of the dihydropyridine group with a high selectivity for arteriolar smooth muscle; it is under clinical investigation for the treatment of hypertension. In this double-blind, randomized crossover trial in 9 patients, the effect of 10 mg felodipine in oral solution on exercise-induced asthma was compared with a placebo on separate days. The FEV1 was at least 80% of the predicted normal value, with variation between study days of less than 10%. Heart rate, blood pressure, and FEV1 were measured before and at 15 and 30 min after each treatment. The exercise test consisted of steady state running at submaximal work loads for 6 to 8 min and started at 30 min after treatments. FEV1 was measured at 1, 2, 5, 10, 15, and 30 min after the end of exercise. The predrug baseline FEV1 values were comparable on the 2 days of the study, and felodipine had no effect on the resting lung function. The mean percentage fall in FEV1 (SEM) after exercise with placebo was 27.0 (4.5)%, and with felodipine it was 13.5 (3.7)%. The difference between felodipine and placebo was statistically significant. While receiving felodipine, the resting heart rate was increased by 15%, with a tendency to lower systolic and diastolic blood pressures. The heart rate after exercise was higher during felodipine treatment than during placebo treatment. One patient receiving placebo and 7 receiving felodipine noted a transient headache. Two patients receiving felodipine also noticed lightheadedness after exercise.(ABSTRACT TRUNCATED AT 250 WORDS)