Expression of genes coding for ubiquitin and heatshock protein (hsp) 70 were examined by in situ hybridization using a rat model with permanent occlusion of the distal middle cerebral artery (MCA). Only polyubiquitin (UbC) mRNA increased markedly following ischaemia in the central zone of the MCA territory of the neocortex. UbC gene expression reached the maximum level 4 h post-occlusion and remained elevated at 24 h. UbC expression was retarded slightly compared with that of the hsp70 gene. UbB and Ub-S30 were expressed at almost similar levels in both the ischaemic and non-ischaemic hemispheres. These results indicated that UbC probably has the most stress-inducible characteristics among the three ubiquitin genes.