This long-term controlled study was undertaken to assess the haemodynamic effects of chronic administration of Nifedipine (N). Twenty patients suffering from pulmonary hypertension secondary to chronic obstructive lung disease were divided into two groups. One group (treatment group) was instructed to take 30 mg of N daily and the other (control group) did not take N. Haemodynamic measurements were recorded before and after an 18-month observation period. For patients in the treatment group, Nifedipine was stopped 24 h prior to the second investigation. Acute response to a single dose of Nifedipine (10 mg sublingually) was also evaluated in all patients during the first and second investigations in order to estimate a possible tachyphylaxis. No significant modification in heart rate, mean pulmonary pressure, mean arterial pressure or blood gases was observed. Conversely, a 10% decrease in cardiac output (p less than 0.05) occurred in the control group. Pulmonary vascular response to acute administration of Nifedipine was the same in both groups before and after the observation period. These results suggest that while long-term administration of Nifedipine to patients with chronic obstructive lung disease does not improve pulmonary pressure, it may prevent a decrease in cardiac output. No tachyphylaxis was noted.