Ischemic preconditioning (IPC) is a phenomenon that a brief episode of ischemia to a tissue renders the tissue resistance from a subsequent prolonged ischemia. It is generally accepted that this protection is a receptor-mediated process, and is realized via signal transduction pathways. Protein kinase C (PKC), known to play key regulatory roles in cellular processes, has been proposed as a primary cellular mediator of preconditioning. However, the role of PKC in eliciting cardioprotection remains controversial. The evidences for the 'PKC hypothesis' of preconditioning in various tissue and organs are summarized. Especially in intestine, a brief ischemia induced a reversible epithelial injury to the jejunum that is associated with activation of several PKC isoforms. Injury induced by an additional period of ischemia is reduced by the prior IPC, and this effect is abolished by non-selective PKC inhibition but not by a selective inhibitor of cPKC/or PKCdelta. This result suggest that activation of nPKC isoform (especially PKCepsilon) during and following ischemic insults may play an important role in protection against I/R injury in the intestine, and this mechanism is identical with previous study in heart tissue.