The effects of ionizing radiation were examined in terminally differentiated cells using nucleated chicken erythrocytes (RBCs) as the model. We used a hemolytic assay to score radiation damage to RBCs. Chicken RBCs received 0 to 100 Gy of radiation at dose rate of 10 Gy/min. Radiation- induced hemolysis occurred in a dose-dependent manner but not immediately after irradiation. Hemolysis became apparent at 24 h after treatment. A threshold for radiation dose response was observed. At doses below 30 Gy, hemolysis in irradiated samples was indistinguishable from that in nonirradiated controls. A total dose of 100 Gy was used for the split-dose experiments. The results showed that chicken RBCs were able to repair radiation damage and that the half-time for maximum recovery was approximately 30 min at 36°C. Recovery from γ radiation was also affected by the interfraction temperature.