Protein kinase C (PKC) is a family of isoenzymes that are serine/threonine kinases implicated in signal transduction pathways controling a wide range of physiological processes such as differentiation, proliferation, gene expression, membrane transport and the organization of cytoskeletal and extracellular matrix proteins. The mesangial  cell in culture provides an excellently characterized cell culture system with well- known signaling pathways. Functional identification of PKC  isoenzymes involved in specific cell responses is one of the most promissing steps towards understanding of molecular mechanisms of cell regulation. In mesangial cells, protein kinase C exerts a bidirectional control function: on the one hand, it activates enzymes like phospholipase A₂, phospholipase D or the mitogen-activated protein kinase cascade to stimulate prostaglandin synthesis, phosphatidylcholine hydrolysis and cell proliferation; on the other hand, PKC terminates signal transmission of the inositol lipid and sphingolipid signaling cascades. This review will illustrate recent developments in PKC regulation and changes in levels, isoforms and activation in renal cells.