To further evaluate the potential utility of lymphocyte beta adrenergic receptor assays in the study of receptor alterations in human disease, we studied highly purified populations of B and T lymphocytes in peripheral blood to see if differences existed in the concentration or affinity of beta adrenergic receptors and catecholamine-responsive cAMP levels. The mean number of receptors present in particulate fractions of B cells did not differ significantly from the number found in T cells. Similarly, no significant difference in the dissociation constant for (-)[3H]dihydroalprenolol was found. Cyclic adenosine monophosphate (cAMP) accumulation in whole lymphocytes as measured by radioimmunoassay was comparable, although a tendency toward lower basal and stimulated levels in the T cells was evident. The data suggest that differences observed in concentrations of beta adrenergic receptors or catecholamine-responsive cAMP accumulation in lymphocytes from patients with varying illnesses are not likely to be due to differences in the proportions of circulating B and T lymphocytes.