The biological UV-dosimeter RoDos is being developed, which weights the UV-radiation according to its DNA damaging potential. The RoDos dosimeter is based on rodent cells growing on a UV-transparent petriPERM(R) foil and a special device which allows irradiation with different doses of W-light, assuring cellular growth under identical spatial arrangement of the cells. Cells under investigation are Chinese hamster ovary cells AA8 (repair proficient) acid UV5 (defective in nucleotide excision repair) grown in monolayer culture. Cells growing on the petriPERM(R) foil were exposed in the RoDos device to increasing doses of WC (254 nm) or simulated sunlight (SSL) of various UVB/UVA proportions. After exposure cells were further incubated for three days, fixed and stained. The influence of irradiation on "cell growth" is determined by image analysis as relative absorbance (A) of the irradiated to unirradiated areas of the petriPERM(R) dish. The resulting action spectra for cell growth inhibition after exposure to simulated sunlight of different qualities were measured with the RoDos device for repair-proficient AA8 cells. The radiation sensitivity of the rodent cell system decreases with longer wavelengths of simulated sunlight, having different proportions of UVB and UVA. (C) 1999 Elsevier Science B.V. All rights reserved.