We report a simple, two-step method (phosphocellulose and immunoaffinity column chromatographies) for purification of the mouse DNA polymerase alpha-primase complex. The advantages of this method over other procedures are its simplicity and rapidity, with little loss by proteolysis. Sedimentation analysis in a glycerol density gradient of the immunoaffinity-purified fraction revealed that four polypeptides with molecular weights of 180,000, 68,000, 54,000 and 46,000 in the enzyme fraction form a physical complex. Peptide mapping by reversed phase-high performance liquid chromatography demonstrated unequivocally that these four polypeptides constituting the complex are different entities.