1. Microtubules prepared from pig brain by two cycles of assembly-disassembly comprise cyclic nucleotide-independent protein kinase activity with phosvitin and troponin T as substrates. 2. Phosphocellulose chromatography resolved two phosvitin kinase activity peaks, one of which coincided with the troponin T kinase peak. 3. The activity peak corresponding to troponin T kinase was inhibited by heparin (I50 = 0.06 micrograms/ml), whereas the other phosvitin kinase peak was unaffected. 4. Both kinase fractions phosphorylated tubulin and microtubule-associated protein (MAP-2). 5. It is concluded that pig brain microtubules contain bound casein kinases I and II. The association may target the action of these kinases toward microtubular proteins in vivo.