Binding sites for angiotensin II (Ang II) and angiotensin converting enzyme (ACE) were studied by autoradiography in human, rat and bovine adrenals and human pheochromocytomas. In human and rat adrenals, binding sites for both Ang II and ACE were found in the medulla and zona glomerulosa. In bovine adrenals, ACE binding sites were not detectable, while Ang II binding was higher in the zona glomerulosa, lower in the rest of the cortex and undetectable in the medulla. In pheochromocytomas, ACE binding was homogeneously distributed, but no Ang II binding was detected. These results suggest that circulating and/or locally formed Ang II could regulate adrenomedullary and zona glomerulosa functions in man, and show that chromaffin cells in tumors retain ACE binding sites but lose Ang II binding sites. Thus, there are alterations in the regulation of the renin-angiotensin system in chromaffin tumors.