A new polycarbonate urethane (PCU-I) was synthesized from aliphatic monomers, i.e. polyhexamethylene carbonate diol and 4,4'-methylene-bis cyclohexane diisocyanate, a mixture of low molecular diols, and castor oil (containing mainly the triglyceride of 12-hydroxyoleic acid). The second synthesized polymer (PCU-II) did not contain castor oil. Both PCUs had good tensile strength, i.e. 32.5 and 27.8 MPa for PCU-I and PCU-II, respectively. Modification by castor oil led to a decrease in glass transition temperature (T(g) = -14 degrees C for PCU-I and -6 degrees C for PCU-II) and an increase in the softening temperature (135 and 125 degrees C for PCU-I and PCU-II, respectively). Partial crosslinking of PCU-I increased the storage modulus of elasticity and provided better resistance to sterilization by ETO and gamma radiation. Both PCUs displayed good stability when subjected to sterilization by hydrogen peroxide plasma. Neither PCU caused cytotoxic effect in mouse fibroblasts (3T3 Balb C). They also had no toxic effects on the morphotic components and did not influence changes in the hematologic parameters or plasmatic coagulation system of human blood.