Thallium-201 brain single-photon emission tomography (201Tl-SPET) is widely used to detect viable tumour tissue with increased metabolic activity. When reperfusion takes place early in cerebrovascular lesions of embolic origin, the presence of tissue areas with increased regional blood flow and preserved metabolic activity can also be assumed. In the present study our purpose was to investigate whether or not foci of 201Tl accumulation occur in reperfused areas with sustained morphological integrity indicated by computed tomography (CT) scans not showing hypodensity in the acute or subacute period. In 16 stroke patients with possible cortical embolic infarction, dual 201Tl and technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO) SPET was performed in both the acute and the subacute period. 99mTc-HMPAO SPET was performed to detect reperfusion. Follow-up CT scans from the same period were also available. In five cases 99mTc-HMPAO SPET ruled out reperfusion and 201Tl SPET was also negative. In four cases 99mTc-HMPAO studies indicated reperfusion early in the acute phase (24-72 h), and comparative CT, without showing hypodensity in the acute or subacute period, also favoured the possibility of sustained metabolic activity. In these cases 201Tl SPET was negative in both the acute and the subacute period. In seven cases CT already showed necrosis in 99mTc-HMPAO hypoperfused areas in the acute period, with negative results on corresponding 201Tl SPET. Later reperfusion occurred in the subacute period (8-14 days) as indicated by 99mTc-HMPAO SPET, at which time an unexpected focal accumulation of 201Tl was detected.(ABSTRACT TRUNCATED AT 250 WORDS)