[en] The same TBI dose of 750 cGy was given to CBA mice either in a single dose at a low dose rate (4 cGy min^-1) (STBI) or in a fractionated regimen (six fractions of 125 cGy three times a day) at a higher dose rate (25 cGy min^-1) (FTBI). No significant differences were observed between the two groups in the first 48 hours after irradiation except in bone marrow cell numbers, probably due to differences in the overall treatment time between the two TBI schedules. After the first 48 hours repopulation patterns of the different cells were very similar in both groups. These findings suggest that different dose rates and fractionation caused similar radiation damage to the murine haemopoietic system. No significant repopulation occurred during the longer overall treatment time of the fractionated regimen. (author)