Aortic segments from 47 New Zealand rabbits were used, of which 14 were denuded of endothelium. Balloon angioplasty was performed on the aortic segments in vitro. The inner surfaces were perfused and the perfusates then given to vessel segments with or without endothelium. The contraction evoked was then counteracted by adding either vasoactive intestinal polypeptide (VIP), substance P (SP), acetylcholine (ACh), or nitroglycerin (NTG) in increasing concentrations. Perfusates from aortic segments with or without endothelium and previously treated with angioplasty induced vasoconstriction of similar magnitude in the segments used for vasomotor investigation irrespective of whether the endothelium was intact in these or not. Endothelial dependent dilators (ACh, SP) did not counteract the contraction whereas endothelial independent dilators did (NTG, VIP). Neither the induction nor the reversal of vessel wall induced vasoconstriction after balloon angioplasty seems to depend on the presence of endothelial cells.