DNA polymerase alpha combined with the endoplasmic reticulum (ER) was isolated from unfertilized sea urchin eggs. NaCl treatment of this fraction released DNA polymerase alpha from the ER. The molecular size (the S value) of the ER-free DNA polymerase alpha changed with the concentration of NaCl used; being 23 S, 11-15 S and 6-8 S in the presence of 0.05-0.12 M, 0.12-0.24 M and more than 0.24 M NaCl. DNA polymerase alpha activity decreased concomitantly with the reduction in molecular size. The 6-8 S form of DNA polymerase alpha did not aggregate by itself nor with other cellular components nonspecifically, when the 23 S form was present. These results are evidence of the presence of 6-8 S DNA polymerase alpha as a high molecular weight form (23 S-form) in sea urchin eggs.