- Members of the protein kinase C (PKC) family of serine/threonine kinases have been implicated in several physiological processes regulating the activation response of platelets. They are involved in processes leading to granule secretion, integrin activation, platelet aggregation and spreading, and procoagulation. The protein kinase C θ (PKCθ) isoform, which was originally identified in T lymphocytes, is also expressed at relatively high levels in platelets, wherein it is involved in the regulation of hemostasis and thrombosis. Recent studies suggest a role for PKCθ in protease-activated receptor (PAR)-, glycoprotein VI (GPVI) receptor- and glycoprotein α(IIb)β(3) integrin receptor-linked signal transduction pathways. The present review focuses on the latest observations relevant to the role of PKCθ in platelet activation.