Intermediate filaments (IFs), major components of the cytoskeleton, undergo dramatic reorganization of their structure during cell signaling and the cell division cycle. This IF reorganization is accompanied by site-specific phosphorylation of IF proteins on serine and threonine residues. Several protein kinases act as IF kinases and regulate spatial and temporal distribution of site-specific IF phosphorylation. Site- and phosphorylation-specific anti-IF antibodies can enable site-specific IF phosphorylation and thereby IF kinase activitiesin vivoto be visualized by immunocytochemistry. Thus, elaborate mechanisms regulating IF phosphorylation together with IF kinase activities are becoming better understood.