[en] Blood samples of ten Chernobyl and one non-Chernobyl victims were analysed both by conventional cytogenetics and by fluorescence in situ hybridization (FISH) using a cocktail of chromosomes 2, 3 and 8. The analysed group comprised men acutely irradiated mainly in 1986 and aged 26-47 years at the time of first blood sampling. All of them displayed acute radiation syndrome of varying severity. Chromosome analysis of the earliest blood samples was carried out by conventional scoring of unstable aberrations with the number of metaphases analysed per individual ranging from 35 to 300. Estimated individual doses ranged from 0.85 to 9.8 G y. After a 10 year delay, i.e. in 1996, blood samples were analysed both by conventional scoring of unstable aberrations and by FISH measurements of stable ones. Usually about 500 metaphases per individual were scored. Estimated by the FISH-method individual translocation (tc + ti) frequencies ranged from 2.2 to 116.8 per 100 cells full genome equivalent. Based on three different published dicentric dose response, in vitro curves individual doses were calculated from the earliest dicentric frequencies. A dose response curve for truly persisting translocations (tc + ti) was estimated over the range 1-10 Gy