A method of reproducibility measuring human leukocyte beta-adrenergic receptor density and affinity has been developed and applied to the study of receptor regulation in man. The method has the advantages of using a membrane preparation which binds highly specifically and employing techniques such as using low concentrations of [3H]dihydroalprenol, analyzing the data by computer modelling techniques, and providing data from both granulocytes and lymphocytes in the same individual to minimize measurement errors. Using this methodology, human beta-adrenergic receptor regulation is examined. Cortisone acetate was found to induce an acute rise in granulocyte beta-adrenergic receptor density and adenylate cyclase activity and an acute fall in lymphocyte beta-adrenergic receptor density. This potentially differential regulation of a single receptor subtype in two lines of leukocytes has important implications for the study of receptor regulation in man using leukocyte models.