No cell type practicably obtainable in vivo, such as blood cells, is known to contain parathyroid hormone (PTH) receptors; this deficiency has hampered investigation of receptor regulation. Second, PTH in vivo is among the potent stimulators of osteoclastic activity, although no direct hormonal effects on these cells have been identified. Several lines of evidence suggest that cells of the immune system may mediate PTH effects on osteoclasts. We, therefore, studied bovine blood cells for the presence of PTH receptors and PTH-stimulated adenylate cyclase. Using an analogue of bovine PTH, ¹²⁵I-labeled [Nle⁸,Nle¹⁸,Tyr³⁴]bPTH-(1--34)amide, we found PTH-specific binding to intact, nonadherent mononuclear cells (lymphocytes) and PTH-stimulated adenylate cyclase in plasma membranes prepared from these cells, and not with cells or membranes from other blood cells. Lymphocytes may serve to study the effects of physiologic and pathologic perturbations on PTH-receptor function in vivo. Exploration of PTH-related lymphocyte responses may help define the relation between cells of the immune system and osteoclastic bone resorption.