Mononuclear leukocytes are easily accessible cells for investigating the regulation of beta-adrenergic receptors in humans. We have previously shown that brief incubations with agonists redistribute (? internalize) most of the beta-adrenergic receptors on mononuclear leukocytes away from the cell surface without changing total receptor number. However, negligible redistribution occurred after exercise or an infusion of isoproterenol. The current study was designed to ask whether receptor redistribution occurs over a longer time course after administration of terbutaline, a beta 2-adrenergic agonist that is known to cause a decrease in receptor number. Normal volunteers were given terbutaline, 5 mg t.i.d. for 6 days. As expected, the number of beta-adrenergic receptors decreased. However, the remaining receptors were not redistributed. Redistribution also did not occur after 1 or 2 days of terbutaline, at which time down regulation was minimal. We also found that terbutaline did not alter the ability of the receptors to be redistributed or desensitized by a preincubation with isoproterenol.