Protein kinase C (PKC) is now known to play an important physiological role in essentially all cell types. This review will focus on what is known about the kinase in contractile differentiated smooth muscle. Current knowledge on the molecular structure of PKC isoforms will be discussed as they relate to mechanisms of translocation and targeting of the kinase within smooth muscle cells. Studies performed on PKC-dependent signalling pathways in differentiated smooth muscle cells will be discussed with emphasis on studies form our laboratory, especially discussing thin filament linked pathways. Thick filament linked PKC-dependent pathways will be described in more detail elsewhere in this monograph.