Tissue distribution studies of [18F]haloperidol and [82Br]bromperidol, two potent neuroleptic drugs, were performed in rats by serial sacrifice. The usefulness of external scintigraphy in obtaining tissue distribution data in large animals is demonstrated by the tissue distribution of [18F]haloperidol in rhesus monkeys. Both serial sacrifice and external scintigraphic studies demonstrated that uptake of the two drugs after intravenous administration into their target organ, the brain, was very fast and that the ratio of brain to blood levels was high throughout the 2-hr observation. Bromperidol appeared to reach peak brain levels faster than its chloro analog, haloperidol. Both bromperidol and haloperidol concentrated overwhelmingly in the rat lung. Haloperidol also showed a high affinity for the monkey lung. The disposition pattern in rats of [18F]-beta-(4-fluorobenzoyl)propionic acid, an apparent intermediate in butyrophenone metabolism, was entirely different from that of the parent drugs. This metabolite did not concentrate in the rat brain.