Aspects of the invention relate to the use of novel oligonucleotides as temperature-sensitive inhibitors for thermostable DNA polymerases. Some inhibitors exhibit temperature-dependent and, in some cases, reversible inhibitory property by changing the conformation of at least a portion of the oligonucleotides from double-stranded to single stranded or in some cases vice versa in a temperature-dependent manner. Aspects also relate to the use of an the inhibitors in a hot-start PCR compositions, wherein the inhibitor may act to suppress the activity of the thermostable DNA polymerase below a desired activation temperature, Tact, and wherein the inhibitor is thermally inactivated above Tact, thus liberating the polymerase activity and initiating the DNA amplification process. Aspects further relate to a procedure for formulating the composition of a hot-start PCR reaction mixture. The hot-start PCR methods disclosed herein are generally faster, more flexible and lower in cost than existing methods.