Thermoplastic properties of fish myofibrillar proteins were studied by dynamic mechanical thermal analysis. Important changes in dynamic mechanical properties, observed when the temperature was increased, were associated with the glass transition of fish myofibrillar proteins. The glass-rubber transition was observed between 215 and 250 degrees C for the dry material. Addition of water or hydrophilic plasticizers (sucrose and sorbitol) induced large decreases in the glass transition temperature. The depressive effect of water content on the glass transition temperature is described with non-linear relationships. The thermodynamic theory of glass transition (i.e. the Couchman-Karasz equation) was adequate to describe partially the plasticizing effect of water on the myofibrillar proteins. Glassy or foamed biopackagings were obtained by a thermomoulding technique when the process temperature was higher than the glass transition temperature at a given moisture content.