Distribution ratios of water-soluble nonelectrolytes have been measured for two systems, human red bood cells/isotonic saline and hemoglobin solutions/water. The results show that for these solutes there is a significant amount of nonsolvent water associated with Hb. However, the amount of this nonsolvent water depends markedly on the temperature, as well as on the size, steric configuration, and functional groups of the probe solutes. The significance of the data is discussed.