Radiosensitivities of ten apparently normal human diploid fibroblast strains to cell killing, G2-phase chromosomal aberrations, and cell cycle delay.

We have examined the sensitivity to X-irradiation of ten apparently normal human fibroblast cell strains received as coded samples. Three different end points were examined: cytotoxicity; induction of chromosomal aberrations after irradiation in G2; and G1-phase block after irradiation and release from confluent growth. Three of these ten strains showed a moderate degree of hypersensitivity to X-rays by all three assays, falling within the range previously reported for ataxia telangiectasia heterozygotes. This variability in the "normal" response may render difficult the use of these techniques in the detection of gene carriers for such disorders in the general population. Furthermore, it indicates that care should be taken in the selection of reference control strains in studies of the sensitivity of cells from various genetic disorders to radiation.