The possibility of the evaluation of ischemia solely by the momentary values of regional cerebral blood flow (rCBF) was investigated. Ischaemic damage was evaluated histopathologically and by observing albumin extravasation. Unilateral carotid clippings were performed for 1 h and the gerbils evaluated with regard to the length of recirculation time. In animals without a recirculation period, the degree of damage could be explained by the rCBF reduction ratio during clipping. However, in cases with reperfusion periods, 5 animals showed an almost complete disappearance of rCBF during clipping, but albumin extravasation was seen in 1 case only. Thus, the discordance between the rCBF reduction ratio and the abnormal permeability was considerable in reperfused animals. The post-ischaemic rCBF pattern was classified into 3 types, the 'post-ischaemic hyperperfusion type', the 'post-ischaemic hypoperfusion type' and the 'post-ischaemic normoperfusion type'. In the first two types, the albumin extravasation was positive in 10/10 cases, and in the third type, in only 1/20. Therefore, the post-ischaemic rCBF pattern was thought to correlate well with ischaemic damage in the reperfused cases. The rCBF changes momentarily and the pattern analysis of the rCBF, particularly in the post-ischaemic phase, appeared to be important.