DNA-polymerase beta was isolated from embryonic cells of the sea urchin S. intermedius and purified 1040-fold. The molecular weight of the enzyme is 40 000, sedimentation coefficient 3.2S, pI 8.5. The SH-reagent--N-ethylmaleimide--has no appreciable influence on the enzyme activity. The enzyme is thermolabile and needs four deoxyribonucleoside triphosphates, bivalent metal ions (Mg2+ or Mn2+) and primer template for its activity. The maximal activity is observed when a synthetic polymer--poly(dA).oligo(dT) is used. DNA-polymerase performs DNA synthesis via a distributive mechanism. In terms of physico-chemical properties, the enzyme can be related to DNA-polymerases beta.