A method was developed for preparing endothelium-denuded resistance arteries (mean internal diameter, 176 microns) from the term fetal lung to be used for tests in vitro. The endothelium was removed mechanically by passing a sandpaper-polished cat whisker through the lumen. Ultrastructurally, the preparation had a well-preserved internal elastic lamina which was facing the lumen without any endothelium superimposed. Its response to contractile agents (excess potassium, a thromboxane A2 analogue, endothelin-1) tended to be greater compared to the intact artery. Conversely, the relaxation to acetylcholine was abolished in the endothelium-denuded artery and, in its place, a modest contraction ensued. Sodium nitroprusside relaxation, unlike acetylcholine relaxation, was affected insignificantly by endothelium denudation. This preparation, in combination with the preparation of the intact resistance artery, is a useful, new tool for studying local factors responsible for pulmonary hemodynamic control in utero and through the transitional period at birth.