Seed accessions stored for more than 20 years in the genebank were evaluated. Seed deterioration was discussed in relation to the low seed moisture content which varies in relation to the drying methods used. The determination of the optimal seed moisture content was based on comparisons between the positive and negative effects of storage using the rate of seed germination after storage depending on the seed moisture content. On the basis of the observed results, the optimum seed moisture for storage at –18°C was suggested. Seeds with high amount of lipids survived better seed moisture content lower than 4%. Leguminous seeds were more sensitive to dry storage, and optimum seed moisture varied between 6.5% and 7.5%. In cereals this value was between 6.1% and 7.2%.