Primer annealing specificity and PCR buffers
Magnesium ion concentration
Various PCR additives or enhancers are available for improving PCR results. It is claimed that these reagents relieve secondary DNA structure (e.g., in GC-rich regions or in long amplification products), lower template melting temperature, enhance enzyme processivity, stabilize DNA polymerases, or prevent attachment of polymerases to plasticware.
Commonly used PCR additives include dimethyl sulfoxide (DMSO), bovine serum albumin (BSA), and glycerol.