Furosemide-induced inhibition of 86Rb uptake was measured in rat and rabbit aorta and compared with its ability to inhibit contractions induced by α-adrenergic agonists. In both rat and rabbit tissues, furosemide defined a portion of 86Rb uptake (IC50 = 2.5 µM) which was distinct from the ouabain-sensitivite fraction. Furosemide-sensitive 86Rb uptake was [Cl–]ext dependent and required Na+ and K+ for optimal activity, suggesting that it reflected a Na+-K+ cotransport process. Furosemide-sensitive 86Rb uptake was found to be greater in HEPES buffer than in bicarbonate buffer. Phenylephrine-induced contractions of rat and rabbit aorta were inhibited by furosemide; however, rat responses were far more sensitive. Agonist-induced uptake of 45Ca was reduced by furosemide in rat aorta, but not in rabbit aorta. Agonist-induced 45Ca efflux stimulation was reduced in both species. These findings indicate the presence in arteries of a furosemide-sensitive, Cl– dependent Na+-K+ cotransport process. Along with other monovalent transport processes, it may modulate Ca2+ availability and thereby influence arterial contract