Previous studies involving large isolated pulmonary arteries have suggested that the administration of high concentrations of natural androgen produces acute vasodilation. This study examines the acute effects of testosterone (T) and dihydrotestosterone (DHT), observed previously in large arteries, in small pulmonary arteries (SPA). Isolated segments of SPA taken from the lungs of Sus domestica (n = 4, mean outside diameter = 313 ± 26 μm) were doubly cannulated and perfused with physiologic saline solution (PSS). The vessels were also simultaneously superfused in PSS and pressurized to 17mmHg. After a period of equilibration, the observed trend of the SPA to both T and DHT appeared to be that of a dose-dependent vasodilation. The concentrations of T and DHT necessary to induce vasodilation in the SPA may be lower than those needed to induce similar responses in large pulmonary arteries.