Cytochrome P-450 specific for steroid 11 beta-hydroxylation (P-45011 beta) was immunohistochemically demonstrated in the adrenal glands of human, pig and bovine and of mineralo- and glucocorticoid excess using a specific monoclonal antibody against P-450 11 beta of bovine adrenocortical mitochondria. P-450 11 beta was present in all three cortical zones of the histologically normal adrenal glands of bovine, pig and human, particularly in the zona fasciculata (ZF) and reticularis (ZR). The P-450 11 beta immunoreactivity was intensive in cortical micronodules and inner ZF and ZR in Cushing's disease, and relatively intensive in the zona glomerulosa (ZG) and outer ZF in idiopathic hyperaldosteronism (IHA), corresponding to the sites of active steroidogenesis. In adenomas with Cushing's syndrome and primary aldosteronism, compact cells were generally stained well. In the adrenal glands attached to the adenomas, immunoreactivity was observed only focally in ZG cells but not in ZF and ZR cells.