Introduction:
The component of commercial available master mix most sensitive to unfavorable conditions is a polymerase. Available commercial polymerase chain reaction (PCR) master mixes are generally recommended for storage at –20°C, otherwise they may lose their activity.

Aim:
The aim of the experiment was to verify if storing mixes in adverse and extreme conditions may influence the quality of a PCR product. In the second phase of the research, it was to indicate if inactive PCR reagents that have lost their activity, may recover their enzymatic properties.

Material and methods:
Five different commercially available master mixes were incubated in unfavorable conditions. After the PCR, an electrophoresis was carried out and the obtained product was an evidence of a proper PCR reaction.

Results and discussion:
Total degradation of mixes was caused by their incubation at room temperature for 28 days and incubation at 100°C for 60 minutes. Addition of polymerases to the degraded mixes (incubation at room temperature for 28 days) resulted in a regeneration of all of five mixes. In the case of polymerases incubated at 1008C for 60 minutes, regeneration was effective only in two of the five mixes.

Conclusions:
Our research confirms that PCR master mix is characterized by high resistance to varied conditions as well as in some cases can be repaired after degradation.