Effects of 2-deoxy-D-glucose (2-DG) and 5-bromo-2-deoxyuridine (BrdU) on 60Co gamma-radiation-induced damage in normal mouse bone marrow have been investigated. Cytogenetic damage as measured by the frequency of cells with micronuclei was studied at various time intervals after irradiation. Intravenous administration of 2-DG (0.1 ml, 1 g/kg body weight) just before or after whole-body irradiation (absorbed dose 2.5 Gy) significantly reduced the micronuclei fraction as compared with irradiated controls. Incorporation of BrdU given intraperitoneally in 13 injections (0.3 ml) (total dose 2 g/kg body weight) at intervals of 1 h increased the micronuclei frequency, but administration of 2-DG significantly decreased cytogenetic damage. The results have interesting implications for improving tumour radiotherapy.