Melting of acrylonitrile polymers (which have a tendency to degrade before melting) was detected during their heat treatments at high heating rates (i.e., 80 degrees C min(-1) or above). The probable reason for their melting at such higher heating rates is discussed. The melting behavior of acrylonitrile polymers was also studied by sealing the polymer with water in a specially designed pressure pan and then heating it in the differential scanning calorimetry cell. The phenomenon of melting is found to be influenced by the rate and environment of heating, molecular weight, and nature of the comonomer. Water suppresses the melting point (T-m) of the polymer due to its plasticization effect; however, it causes the hydrolysis of some CN groups during this process of melting. The nature of melting endotherm has been correlated with the structure of the polymer.