Objective: The evaluation of pulmonary vascular reactivity plays a significant role in the management of patients with pulmonary hypertension. Inhaled nitric oxide in combination with oxygen (O-2) has become widely used as an agent for pulmonary vasodilator testing. However, inhaled nitric oxide is not available in many developing countries. Recently, aerosolized iloprost was suggested as an alternative to nitric oxide for this purpose. In the present study, aerosolized iloprost was used together with O-2 in the pulmonary vasoreactivity test of children with severe pulmonary hypertension. Thus, the synergistic effect of both vasodilators was utilized without extending the duration of cardiac catheterization.