Folding primer (FP), together with turn-back primer (TP) and boost primer (BP), is one of the major components of SmartArnp2, a rapid amplification-based method for SNP detection. FP has a unique design where the annealing region is combined with a tail that can fold back. FP tails can be classified as either "strong" or "weak", depending on the melting temperature and free energy of the hairpin structure. We report that FP tails affect the amplification process differently; by changing the FP concentration we can, increase the amplification reaction speed with "strong tails". Unlike "strong tails", concentration change of FP with "weak tails" did not show significant impact on the amplification speed. The comparative analyses using gel electrophoresis demonstrate that the FP type and FP ratio in the reaction change the amplification pattern. The above observations can be used to optimize the reaction and manipulate the reaction speed of SmartAmp2. (C) 2009 Elsevier Inc. All rights reserved.