To investigate the mechanism of receptor changes associated with aging, we developed a beta-adrenergic receptor assay in whole human lymphocytes which fulfills strict affinity, stereospecificity, and specificity criteria. Lymphocyte beta-adrenergic receptors were quantified in 54 (36 males and 18 females) healthy subjects on no medications divided into two age groups, 18 to 30 years (mean: 24) and 60 to 72 years (mean: 64). Using this assay, we report no change in the number of lymphocyte betaadrenergic receptors in elderly (mean ± SE: 801 ± 114 sites/cell) compared to young individuals (680 ± 47). When the values are examined separately for males and females there again is no significant difference between younger and older groups. We, therefore, suggest that further investigation is necessary before decreased hormonal responsiveness in the elderly is ascribed to decreased hormone receptor number on the basis of lymphocyte beta-adrenergic receptors.