The binding characteristics of platelet .alpha.2-adrenoceptors, lymphocyte .beta.2-adrenoceptors and platelet imipramine receptors were studied in five women during their menstrual cycle. A significant cycle variation in the number of .beta.2-adrenoceptor sites on intact lymphocytes was found during the menstrual cycle, while binding to .alpha.2-adrenoceptors and imipramine receptors remained unchanged.