Inner muscle of sheep carotid arteries responded to norepinephrine in lower concentration, and with a larger initial contraction, than outer muscle. Initial contractions of both tissues did not require external Ca but stable contractions did. Papaverine greatly depressed stable but not initial contractions, causing inner muscle to respond to each effective concentration of norepinephrine by contraction followed by relaxation. Papaverine particularly depressed the stable responses of inner muscle to low concentrations of norepinephrine. Nitrite generally caused changes in response qualitatively similar to those produced by papaverine.