A formulation and kit of thermostable or other DNA polymerases comprising at least one thermostable or other DNA polymerase which lacks 3′-exonuclease activity, and at least one thermostable DNA polymerase exhibiting 3′-exonuclease activity. Also provided is an improved method for enzymatic extension of DNA strands, especially while, but not limited to, amplifying nucleic acid sequences by polymerase chain reaction wherein the above formulation is made and used to catalyze primer extension.