Upon stimulation of a cell surface receptor, a membrane phospholipid degradation cascade is often induced through the activation of several phospholipases, yielding various lipid metabolites such as diacylglycerol, free fatty acids, lysophospholipids, and phosphatidic acid. Several isoforms of protein kinase C are each activated distinctly by various combinations of the lipid metabolites, presumably in different subcellular compartments. The pivotal role of this enzyme family in the intracellular signaling network is beginning to emerge.