The invention provides compositions containing a mixture of (a) an enzyme that possesses substantial 3'-5' exonuclease activity (b) a DNA polymerase with less 3'-5' exonuclease activity than the enzyme with substantial 3'-5' exonuclease activity. Preferably, the DNA polymerase for inclusion in the compositions are DNA polymerases that substantially lack 3'-5' exonuclease activity. A preferred embodiment of the invention is a composition comprising Taq DNA polymerase (isolated from Thermus aquaticus) and Pfu DNA polymerase (isolated from Pvrococcus furiosus). Another aspect of the invention is to provide methods for synthesizing polynucleotides using compositions comprising an enzyme that possesses substantial 3'-5' exonuclease activity and a DNA polymerase with less 3'-5' exonuclease activity than the enzymes possessing substantial 3'-5' exonuclease activity, preferably a DNA polymerase that substantially lacks 3'-5' exonuclease activity. Another aspect involves the use the subject method of polynucleotide synthesis to carry out the synthesis step in a polymerase chain reaction experiment.