In this study the stability of PON1 activity has been tested in human serum samples during storage up to 12？months at 3 commonly used temperatures, -20°C, -70°C and ？196°C. It was found that the stability of the PON1 activity is constant during 12？months of storage at ？70°C and ？196°C. Storage at ？20°C resulted in a small but statistically significant decrease after 6？months to about 94% of its original value. Nonetheless, the rank order between the samples at T？=？0 and 12？months remained the same. The same temperature dependence was found for the associated high-density lipoprotein.It can be concluded that ？70°C is the right temperature for storage to maintain the PON1 activity for at least one year. Storage at a lower temperature in liquid nitrogen (？196°C) is not necessary.