The cell cycle regulating Cdc2 protein kinase helps orchestrate cell cycle dependent changes in cell structure and function. This report shows that Cdc2 is localized to the centrosome region and is tightly bound to the nuclear matrix-intermediate filament scaffold. Antibodies to Cdc2 and to the centrosome-specific protein, pericentrin, label the centrosome in an apparently cell cycle independent manner. Isolated centrosomes also label similarly with both antibodies. Essentially, all cells show Cdc2 labeling of the centrosomes, implying an independence of the stage in the cell cycle, a conclusion supported by studies of synchronized cells. In contrast to the labeling of every cell with the Cdc2 monoclonal antibody, fewer centrosomes were labeled with an antibody to the PSTAIRE domain of Cdc2. Embedment-free, immunogold electron micrographs of extracted cell whole mounts show the centrioles and a pericentriolar network of filaments. Both Cdc2 and pericentrin antibodies decorate the amorphous pericentriolar material, while the Cdc2 antibodies also decorate the centrioles themselves. The constitutive presence of Cdc2 at the centrosome suggests a continuing role in the dynamics of centrosome function throughout the cell cycle.