Twenty-six hypertensive patients took part in an open, randomized, parallel-group pilot study of the effects of a nine-week treatment period with the calcium antagonist isradipine and the beta-1-blocking agent atenolol. The mean dosage in the isradipine group was 7.9 +/- 3.5 mg/day, and 69.2 +/- 43.5 mg/day in the atenolol group. A significant reduction of the arterial blood pressure was seen with both treatment regimens. Lung volumes and airways resistance remained unchanged, but, in the atenolol-treated group, the linear relationship between alveolar pressure and airways resistance at the lower lung volume during forced expiration at 25% of forced vital capacity was affected by a shift to higher airways resistance. This change can be interpreted as an early sign of altered air-flow behavior in the small airways in subjects susceptible to beta-adrenoceptor blockade. The calcium antagonist isradipine did not produce changes in any parameters of lung function in this group of patients.