The adverse functional effects of balloon angioplasty include simple procedure failure, compromise of vessel lumen (rupture), and restenosis. A much less well-defined repercussion of balloon injury to arteries is a paradoxical alteration in vascular reactivity at an anatomically distant site. The paper by Accorsi-Mendonça in the current issue presents new data showing that, following balloon injury to the rat left common carotid artery, there is a delayed hyperreactivity to both phenylephrine and angiotensin II in the contralateral artery. The pharmacological basis of these effects is unknown, although the authors demonstrate that products of cyclooxygenase (COX) 1 or 2 are responsible for the hyperreactivity to angiotensin II and phenylephrine, respectively. The absence of delayed hyperreactivity to these agents in the aorta of injured rats would suggest that a humoral factor is not involved.