Exposure of cells to ionizing radiation gives rise to DNA damage, comprising strand breaks and base modifications. All these lesions may contribute to cell death, mutagenesis and/or carcinogenesis, but their relative contributions are likely to be different. It is important, therefore, to study the various damages with respect to their abundance and persistence. To detect radiation-induced DNA damage, the alkaline-elution technique was applied. In a flanking comparative study, a newly developed immunochemical assay was used. Mice were irradiated with X-rays (8 or 12 Gy) and killed at different time intervals after the irradiation. Total white blood cells and bone-marrow were isolated, and the different types of DNA damage determined. Murine blood and bone-marrow cells, as well as human blood, were irradiated in vitro and subsequently incubated at 37 degrees C for different time periods, followed by analysis of radiation-induced DNA damage. Also, white blood cells from leukemia patients receiving chemo- and radiotherapy (total-body irradiation) were investigated, to study the in vivo induction and repair of DNA lesions in humans. With both techniques used, the proportion of DNA damage remaining in blood cells of mice after in vitro or in vivo irradiation and subsequent repair was found to be larger than that in human blood cells after in vivo or in vitro irradiation and repair.