We report the hemodynamic and clinical effects of acute and chronic administration of iloprost in two patients with severe pulmonary hypertension caused by toxic oil syndrome. We tested the acute effect of progressive increments of iloprost, followed by long-term infusion of the drug during 14 days. The acute response produced an increase in cardiac output and moderate reduction in pulmonary vascular resistance, with no change in pulmonary artery pressure. Nevertheless, a maintained reduction in pulmonary artery pressure and resistance, as well as clinical improvement, was observed after chronic infusion. We conclude that (1) the acute effect of iloprost does not necessarily predict long-term hemodynamic response, and (2) iloprost given in long-term infusion seems to have been an efficacious and safe drug in our two patients, and it opens a new line of treatment.