Protein kinase C (PKC) comprises a large family of serine/threonine kinases which are activated by many extracellular signals. Inside the cell, PKCs are regulated by a variety of lipid second messengers, including the ubiquitous diacylglycerol and phosphatidylserine. Phosphorylation has also emerged as an important mechanism of regulation of all PKCs. Work in the last 20 years has provided evidence that these enzymes are involved in a multitude of physiological processes. Similarly, a number of proteins which are phosphorylated by PKCs have also been discovered and their role in cell biology has been investigated. More recently, there has been considerable interest in a number of specific PKC isoforms and their role in signaling pathways in the cell. This review will focus on recent findings on the mechanism of regulation of PKCepsilon, PKCmu and PKCzeta, and how these enzymes regulate cell growth, the actin cytoskeleton, apoptosis and other biological functions.