* Increase template amount. Sample concentration may be too low. * Template DNA may be damaged. Use carefully purified template. * Lengthen extension time. * Increase the number of cycles. * Lower annealing temperature. * Titrate DMSO (2-8%) in the reaction. * Denaturation temperature may be too low. Optimal denaturation temperature for most templates is 98°C or higher. * Denaturation time may be too long or too short. Optimize the denaturation time.