Protein phosphorylation and dephosphorylation mediated by protein kinases and protein phosphatases, respectively, represent essential steps in a variety of vital neuronal processes that could affect susceptibility to ischemic stroke. In this study, the role of the neuron-specific γ isoform of protein kinase C (γPKC) in reversible focal ischemia was examined using mutant mice in which the gene for γPKC was knockedout (γPKC-KO). A period of 150 minutes of unilateral middle cerebral artery and common carotid artery (MCA/CCA) occlusion followed by 21.5 hours of reperfusion resulted in significantly larger (P < 0.005) infarct volumes (n = 10; 31.1 ± 4.2 mm³) in γPKC-KO than in wild-type (WT) animals (n = 12; 22.6 ± 7.4 mm³). To control for possible differences related to genetic background, the authors analyzed Balb/cJ, C57BL/6J, and 129SVJ WT in the MCA/CCA model of focal ischemia. No significant differences in stroke volume were detected between these WT strains. Impaired substrate phosphorylation as a consequence of γPKC-KO might be corrected by inhibition of protein dephosphorylation. To test this possibility, γPKC-KO mice were treated with the protein phosphatase 2B (calcineurin) inhibitor, FK-506, before ischemia. FK-506 reduced (P < 0.008) the infarct volume in γPKC-KO mice (n = 7; 24.6 ± 4.6 mm³), but at this dose in this model, had no effect on the infarct volume in WT mice (n = 7; 20.5 ± 10.7 mm³). These results indicate that γPKC plays some neuroprotective role in reversible focal ischemia.