Of the total extractable DNA polymerase .alpha., 84% activity was associated with nuclei isolated from mouse myeloma MOPC 104E cells in the presence of Ca2+. From the nuclei, DNA polymerase .alpha. was extracted from these nuclei in the 3 separate steps: activity I, KCl free medium (minus Ca2+); II, 100 mM KCl; III, 200 mM KCl. Partially purified DNA polymerase .alpha. was eluted from a native or denatured DNA-cellulose column by 100 mM KCl. This conforms to the KCl concentration required to extract activity II from nuclei. Activity II may be bound to the DNA in the nucleus. The activity I may be in a free form. After extraction, activity III was eluted from DNA-cellulose by the same KCl concentration as were I or II. Activity III apparently did not have a stronger binding ability than I or II to DNA. Activity III may be present in nucleus by binding to specific sites of DNA or its making a complex with some factor(s). The KCl concentrations required to extract DNA polymerase .beta. and .gamma. conformed to those required to elute these enzymes from a DNA-cellulose column. Most DNA polymerase .beta. and nuclear DNA polymerase .gamma. apparently made a complex with the DNA in nuclei. DNA polymerase .alpha. was resolved into 3 active forms, A, B and C in the order of their elution from DEAE-cellulose as described previously. The activity I described above was composed mainly of form C while the major activity of II and III was form B. The DNA polymerase .alpha. present in the cytoplasm soluble fraction contained forms A and C. Form B of .alpha.-polymerase forms a complex with some nuclear structure, presumably DNA, and probably is an active form involved in DNA synthesis.