Abstract: Disclosed is the radiohalolabelling of metyrapone (1-propanone-1,2-di-(3-pyridinyl)-2-methyl), an 11Beta-hydroxylase inhibitor and of related compounds to form imaging agents for the adrenal cortex. Metyrapone was selectively converted to its mono-N-oxide. 4'-Bromo-metyrapone was obtained therefrom by a three-step conversion. Exchange labelling of the latter gave radiolabelled metyrapone. Found suitable as imaging agents are .sup.77 Br-4-bromo-metyrapone; .sup.131 l-4-iodo-metyrapone; .sup.123 l-4-iodometyrapone and their corresponding metyrapoles. Mixtures of these also can be used as imaging agents.