The advantages of long-term administration of vasodilators in the treatment of chronic cor pulmonale were investigated after informed consent in 60 patients with obstructive respiratory insufficiency (56 men, 4 women, mean age 63.5 +/- 1.5 years; mean pulmonary pressure 30.4 mm Hg). They were randomly divided into two groups of 30, a control group and a group treated with nifedipine, 10 mg three times a day. The following parameters were recorded every 3 months for a year: dyspnea, degree of right ventricular failure, number of days spent in hospital, survival and arterial blood gas tension. On the first day of study, no significant difference existed between the control and the treated groups. After 1 year 22 patients in the control group were still followed and 8 were dead. In the treated group 19 were followed, 7 were dead and 4 stopped treatment, generally due to ankle edema. At the end of the study, the only significant modification was improvement of the dyspnea in the nifedipine group (p less than 0.01). In conclusion, in spite of an improvement in the dyspnea index, clinical study for 1 year failed to demonstrate any objective benefit of nifedipine treatment.