Protein kinase C delta (PKC delta) is a member of the protein kinase C (PKC) family of serine-threonine kinases. It is a 79 kd protein kinase that shows strict dependence on the presence of phospholipids, but shows no activation by Ca2+. Phosphatidylinositol is the most potent activator of PKC delta. Apparent kinetic constants for synthetic oligopeptides (MBP4-14, EGFR peptide and epsilon-peptide) are quite different between PKC delta and other PKCs. Northern blot analysis indicated that PKC delta is widely distributed in almost all the tissues and is a major isoform of PKC expressed in hemopoietic cells. PKC delta is involved in fundamental cellular functions regulated by diacylglycerols and mimicked by phorbol esters. PKC delta is partially associated with the insoluble fraction in cells even in the absence of phorbol 12-myristate 13-acetate (PMA). Upon PMA stimulation, PKC delta translocates to the insoluble fraction of cell homogenates. Overexpression of PKC-delta induces significant changes in morphology and causes the cells to grow more slowly and to a decreased cell density in confluent cultures. These changes are accentuated by treatment with PMA. None of the PKC-delta overexpressers grow in soft agar with or without PMA.