We studied neuropeptide Y (NPY) binding sites in the bovine adrenal gland by incubating tissue sections with [125I]-Bolton Hunter NPY, and then by measuring the number and affinity of binding sites in the tissue with quantitative autoradiography. Specific NPY binding sites were localized exclusively in the zona glomerulosa. These binding sites have an apparent dissociation constant (Kd) of 0.45 ± 0.06 nM and a binding capacity (Bmax of 134 ± 15 fmol mg–1 protein. Our results suggest that NPY may directly affect the release of aldosterone in the zona glomerulosa of the adrenal gl