Primary pulmonary hypertension is an uncommon but serious disease that often results in debilitating symptoms and early death. One approach to treatment has been to attempt a reduction of pulmonary artery pressure and vascular resistance by using vasodilator drugs with conflicting results in several studies. The aim of this study is to review the ten-years (1978-1988) experience of vasodilator therapy for primary pulmonary hypertension at our institute. In this period 7 patients, 5 women and 2 men, mean age 38.4 years (range 15-66) met clinical and hemodynamic criteria for primary pulmonary hypertension. At diagnosis 3/7 patients were in NYHA class III and 2/7 in class II. Diagnosis was confirmed by open lung biopsy in one case. Mean pulmonary artery pressure was 66 +/- 17 mmHg, mean value of pulmonary vascular resistances was 22.5 +/- 11 U.W. and of cardiac index 1.8 +/- 0.58 l/min/m2. Twelve different vasodilator drugs were tested during right heart catheterization in a non randomized manner. Various vasodilators were usually tested in the same patient (2 or more drugs in 6 patients). Only one patient did not tolerate acute therapy because of development of a persistent systemic hypotension. Hemodynamic responses to nitrates showed a general reduction in pulmonary artery pressure and pulmonary vascular resistances with marginal changes in cardiac index. Calcium channel-blocking agents elicited different responses in similar patients with favorable, little, no or adverse effects in pulmonary hemodynamics and sometimes a significant decrease in systemic vascular resistances. Also hydralazine showed favorable hemodynamic results in few cases but exacerbated pulmonary hypertension in others.(ABSTRACT TRUNCATED AT 250 WORDS)