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 reduction of pulmonary arterial pressure and right ventricular afterload by using vasodilator agents to decrease pulmonary arteriolar resistance. Use of a variety of vasodilators has yielded only limited and infrequent success. Although an occasional patient may respond to vasodilator therapy with improved pulmonary hemodynamics and symptomatic status, most patients do not. Reasons for lack of success include the presence of predominantly fixed vascular obstructive disease rather than active vasoconstriction, inexorable progression of disease, and adverse nonpulmonary vascular effects of vasodilators, such as systemic hypotension. Because of occasional beneficial responses, a trial of vasodilators is warranted in patients with primary pulmonary hypertension. Initiation of drug therapy should be undertaken during hemodynamic monitoring in order to allow assessment of response, identification of adverse effects, and comparison of different agents. No vasodilator is clearly superior in primary pulmonary hypertension.