This work was to explore γ-ray induced radioadaptive response(RAR) in Chinese hamster ovary(CHO) cell lines of different DNA damage repair capacities.CHO-9 cells and the two repair-deficient strains

EM-C11(DNA single strand break repair deficient) and XR-C1(DNA double strand break repair deficient)

were irradiated with a priming dose of 0.08 Gy or 0.016 Gy.After 4 or 7 hours

they were irradiated again with a challenging dose of 1 Gy.The micronucleus induction and plating efficiency of the cells were assayed.Under 0.08 Gy priming dose and 4-h interval

just the CHO-9 cells showed RAR

while with the 7-h interval the CHO-9 and EM-C11 showed RAR

but XR-C1 did not.When the cells were pretreated with a lower priming dose of 0.016 Gy in a 4-h time interval

all the three cell lines showed RAR to subsequent 1 Gy irradiation.It can be concluded that RAR is not only related to the priming dose and time interval

but also has close dependence on the ability of DNA damage repair.