D.s.c. analysis shows that heat absorbed in the heating process of water in poly(vinyl alcohol) membranes is higher than that evolved in the cooling process. A remarkable discrepancy is found between these heats when the water retention, H, of the membrane is lower than 0.5 g H2O/g swollen membrane. The amounts of freezable water in the membranes were estimated by use of the relation observed between the temperature and the enthalpy of the crystallization of super-cooled water. The amounts estimated from the heats absorbed or evolved agree within 2% when H was above 0.6. When H is below 0.5, however, the ratio of these two amounts was greater than 2. This difference is explained by the heat capacity of the water below 250 K increasing anomalously compared with that of bulk water.