Critical examination of previous work on the viability of cereal seeds shows that there is a simple mathematical relationship between temperature, moisture content, and period of viability. There is evidence that this relationship is similar for wheat, barley, and oats. If the moisture content and temperature of the seed is known it is possible to predict the expected life of the seed; or alternatively, it is possible to predict various combinations of storage conditions necessary to achieve a required period of viability. These results are discussed in relation to current theories concerned with factors which cause loss of viability in seeds.