The mechanism of selective vulnerability of the cerebral white matter and pallidum in acute carbon monoxide (CO) poisoning was experimentally investigated by measuring regional cerebral blood flow (rCBF) with the iodo-[14C]antipyrine method. A CO group consisting of five cats was exposed to 0.2%-0.3% CO gas and the rCBF was measured when moderate systemic hypotension (70-80 mm Hg) occurred; because systemic hypotension of this level during exposing to 0.2%-0.3% CO gas induces typical cerebral lesions of acute CO poisoning in almost all cats [Okeda et al. Acta Neuropathol (Berl) 54:1-10 (1981)]. Controls were a hypotension group of three cats with moderate systemic hypotension induced for 1 h without CO exposure, and a control group of five cats which inhaled only air for 2 h. The rCBF of each structure in the CO and hypotension groups was evaluated as a percentage of that of the control group. The rCBF of the CO group exhibited a wide range (68%-127%) according to the structures examined, and the mean (94.6%) was large compared with that (range: 53%-82%, mean: 67.4%) of the hypotension group. In the CO group, the examined brain structures where divided in two groups according to the rCBF values; low-value structures and high-value structures. There was significant (P less than 0.05) difference between rCBFs of both the structure groups. The cerebral white matter and pallidum belonged to low-value structures, and these rCBFs did not show any significant difference from those of other structures in this structure group.(ABSTRACT TRUNCATED AT 250 WORDS)