[en] Background and purpose. The aim of the present study was to estimate yields of radiation-induced translocations in surviving cells of several human tumor cell lines and in normal diploid human fibroblasts, and to compare these yields with corresponding intrinsic radiosensitivities determined by standard colony-formation assay. Material and methods. The yields of radiation-induced reciprocal translocations were investigated by fluorescence in situ hybridization. Chromosomes no. 1 and no. 4 were 'painted' with fluorescent hybridization probes for whole chromosomes. Translocation yields and cell survival were determined for different doses up to 6 Gy of 200 kV X-rays. Results. We observed a higher frequency of reciprocal translocations in the radiosensitive cells MCF-7 and MDA-MB-436 than in the radioresistant cells CaSki, WiDr, A549 and normal skin fibroblasts. For primary squamous cell carcinoma cells, ZMK-1, an intermediate radiosensitivity and an intermediate translocation yield were observed. The dose-dependence of translocation yields involving chromosomes no. 1 or no. 4 varied in different cell lines: it was linear or linear with a plateau at higher doses. Conclusions. A comparison of the data obtained with chromosomes no. 1 and no. 4 in the investigated cell types, indicates that intrinsic radiosensitivity of different tumor cells observed at the survival level, is correlated with different translocation yields, respectively. This correlation was observed for all cell types investigated, independent of the number of copies of the painted chromosome per cell or the radiation dose. However, for low doses (under 1 Gy), the yields of translocations determined for the individual chromosomes seem to be too low for a discrimination between radioresistant or radiosensitive cells