Recombinant DNA sequences encoding a thermostable DNA polymerase from Thermus aquaticus can be used to produce a recombinant protein with a molecular weight of about 86,000-95,000 daltons. The thermostable recombinant enzyme can be used in a temperature-cycling chain reaction wherein at least one nucleic acid sequence is amplified in quantity from an existing sequence with the aid of selected primers and nucleotide triphosphates. The enzyme is preferably stored in a buffer containing non-ionic detergents that lends stability to the enzyme.