The recently described pseudorabies virus protein kinase has been purified from infected hamster fibroblasts by a combination of anion-exchange, hydrophobic-interaction and affinity chromatography. The purification resulted in enzyme with a specific activity in excess of 1,000 nmol phosphate mg-1 min-1 in relatively high yield. Gel electrophoresis of the purified enzyme under denaturing conditions revealed a single stained band at a position of migration corresponding to a Mr 38,000. Incubation of the purified enzyme with [gamma-32P]ATP in the absence of added substrate resulted in incorporation of 32P into this protein band, consistent with the 38-kDa protein being a protein kinase with a capacity for autophosphorylation. The phosphorylated form of the protein has an isoelectric point of approximately 4.9. Gel permeation chromatography of the purified enzyme indicated a native Mr 70,000, suggesting that the protein kinase has a homodimeric structure.