This protocol describes assaying kinase activity of a putative kinase using Histone H1 as the substrate. Histone H1 is the canonical kinase substrate in this type of assay. Phosphorylation of Histone H1 is assessed by SDS-Polyacrylamide gel electrophoresis followed by autoradiography. Includes information: H1 Kinase Assay on Individual Xenopus Oocytes; H1 Kinase Assay on Xenopus Egg Extract Samples; H1 Kinase Assay on Tissue Culture Cells; Helpful protocol hints.