The effect of cultivation and dehydration conditions on the adenosine phosphate content of yeast cells has been studied. Irrespective of the cultivation conditions the total pool of adenosine phosphates was found to increase, mainly due to accumulation of ATP, during the exponential phase of cell growth and to decrease during transition of the culture into the stationary phase. Changes in the intracellular content of adenosine phosphates were parallel with changes in the respiratory activity of yeast cells cultivated under batch conditions. Yeast cells harvested at the exponential growth phase were sensitive to dehydration, losing a notable amount of adenosine phosphates as well as respiratory capacity during drying, leading to a massive dying-off of the cells. Yeast at the stationary phase was resistant to drying, and, during this process, accumulated ATP by mitochondrial oxidation of endogenous carbohydrates. The accumulated ATP was used by the dried yeast cells as an energy source in the first minutes of reactivation. On the basis of our results we recommend that the ATP content of dried yeast cells should be used as an indicator of their capacity to recover their viability by reactivation.