γ-Ray sensitivity for cell killing was assayed in 54 human cell strains, including some derived from individuals suffering from certain heritable diseases. The overall range of D₀ values in this study was 38 to 180 rads, indicating a considerable range of variability in humans. The normal sensitivity was described by a range of D₀ values of 97 to 180 rads. All ten ataxia telangiectasia cell strains tested proved radiosensitive and gave a mean D₀ value of 57 ± 15 (S.E.) rads, and these represent the most radiosensitive human skin fibroblasts currently available. Representative cell strains from familial retinoblastoma, Fanconi's anemia, and Hutchinson-Gilford progeria occupied positions of intermediate sensitivity, as did one of two ataxia telangiectasia heterozygotes.

Six xeroderma pigmentosum cell strains together with two Cockayne's syndrome cell strains (all known to be sensitive to ultraviolet light) fell into the normal range, indicating an absence of cross-sensitivity between ultraviolet light and γ-irradiation.