Effect of norepinephrine on contractile force of isolated human turbinate smooth muscle was investigated in this experiment. The results were as follows ; 1) In chronically phenylephrine-exposed preparations, ED50 of norepinephrine for contraction of human nasal smooth muscle was significantly increased compared with control preparations. 2) In these preparations, the maximum reponse was significantly decreased. 3) The pA2 value(the affinity index of antagonist) was significantly decreased in chronically phenylephrine exposed preparations. From these results, it is suggested that the change of responsiveness of human nasal smooth muscle to norepinephrine induced by chronic phenylephrine exposure is possible due to the change of number or affinity of alpha-adrenergic receptors.