Although sildenafil, an oral phosphodiesterase type-5 inhibitor, may offer benefits in the pharmacological management of pulmonary hypertension (PH), safety and effectiveness have not been studied during coadministration with beraprost, an oral prostacyclin analogue. To address this issue, we administered oral beraprost (40 microg) on day 1 and beraprost (40 microg) plus sildenafil (25 mg) on days 2 to 6 patients with moderate to severe PH. Although sildenafil plus beraprost produced transient flushing in 2 of 6 patients, systemic hemodynamics and arterial and venous gas analyses were similar in comparisons between the 2 treatment groups. In contrast, sildenafil plus beraprost therapy resulted in a 2.2-fold greater reduction in mean pulmonary arterial pressure and a 1.6-fold greater reduction in pulmonary vascular resistance compared with beraprost alone, and reductions in these parameters persisted longer with combination therapy than with beraprost alone. Addition of oral sildenafil to beraprost appears to represent a safe and effective therapeutic option, at least in the acute phase, for patients with pulmonary hypertension.