Human alveolar macrophages obtained by bronchoalveolar lavage were studied with the high specific activity β-adrenergic ligand [¹²⁵I]pindolol and found to possess a moderate density of β-adrenergic receptors. Using macrophage membranes, the receptor density (Bmax) was 42 ± 9 fmol/mg protein with an apparent equilibrium dissociation constant (K_d) of 44 ± 9 pM (mean ± SEM). With intact macrophages, the Bmax = 5,643 ± 942 sites/cell with K_d = 29 ± 9 pM. Competition binding studies with subtype-specific antagonists revealed an exclusive population of β₂-adrenergic receptors. Incubation of intact macrophages with the β-adrenergic agonist isoproterenol caused a 6-fold increase in intracellular cyclic AMP (cAMP). Prostaglandin E₁ and forskolin, which activate adenylate cyclase via different mechanisms, afforded typical marked increases in macrophage cAMP. Saturation binding, competition binding, and cAMP accumulation studies may all be performed from a single sample of about 2 × 10⁷ cells, which can be obtained by bronchoalveolar lavage. This should facilitate studies of in vivo regulation of human alveolar macrophage β-adrenergic receptors with regard to immune function and mediator release, and as a possible reflection of lung parenchymal receptors.