The effect of storage conditions on the serological activity of two isolates of potato virus Y-NTN strain (PVYNTN) was studied by ELISA. Purified virus, intact and homogenized infected leaves stored freeze-dried and frozen at various temperatures were tested. Purified virus was the most stable at +4 degreesC and non-purified virus was best preserved as a freeze-dried leaf homogenate at -20degreesC. Their serological activity did not change after three months of storage.