We examined the expression of protein kinase C isoforms in infarcted tissue, penumbra and contralateral brain tissue from 10 patients who died between 1-52 days after ischaemic stroke. Ten patients aged 61-89 years were used in the study. Tissue samples were assayed for protein kinase C activity using a non-radioactive method, and specific isoforms expression determined by Western blotting and staining with anti-PKC polyclonal antibodies. There was a 2-24 fold increase in PKC gamma in the ischaemic penumbra of nine out of 10 patients compared to contralateral tissue. In infarcted tissue expression of PKC gamma was not significantly changed in any of 10 samples but the beta I isoform increased in eight and the beta II in nine patients. There was no significant change in expression in PKC alpha or in infarct or penumbra. Differences in total PKC activity were not specific in seven out of eight patients and it is difficult to estimate their significance. In conclusion after ischaemia there was an altered expression of PKC isoforms with an increase of PKC gamma in the surviving penumbra and beta I and beta II in the infarcted core.