A purified thermostable enzyme is derived from the thermophilic archaebacterium Thermococcus gorgonarius. The enzyme can be native or recombinant, retains approximately 90% of its activity after incubation for two hours at 95.degree. C. in the presence of stabilizing agents and possesses 3'-5' proofreading exonuclease activity. Thermostable DNA polymerases are useful in many recombinant DNA techniques, especially nucleic acid amplification by the polymerase chain reaction (PCR).