PKC is composed of an ever growing family of lipid dependent serine/threonine protein kinases. Collectively, these isoenzymes are known to mediate critical roles in signal transduction, tumour promotion and cell regulation. PKCs appear to function as switches in acute signal transduction paradigms as well as rheostats in long term cell regulation with multiple mechanisms operating in the regulation of these functions. Although these roles of PKC are well established, little is known about the regulation and roles of individual isoenzymes of PKC in vitro or in vivo.