Abstract: Purpose : To evaluate the cytogenetic effect of irradiation on the workers , early engaged in X-ray medicine in China , who had been exposed to X-ray at low dose rate for a long time (22244 years) . Method : The peripheral lymphocyte chromosome aberrations f rom 25 medical X-ray workers and 10 cont rols were analyzed by fluorescence in situ hybridization ( FISH) with probes of chromosomes 4 and 7 and verified with Giemsa staining. Results : The normal target chromosomes and their aberration were directly exhibited in morphology. The chromosomes translocations of X-ray workers were 84 % of all chromosome aberrations in this group. Ins (in-sertion) , Dic (dicent ric) and Ace (acent ric f ragment) were 1. 9 % , 4. 5 % and 9. 7 % , respectively. The f requencies of chromosome t ranslocation and total aberrations in X-ray workers were higher than that of the cont rol group ( P < 0. 005) . Conclusion : The peripheral lymphocyte of medical X-ray workers exists chromosomes aber-rations , the most part of which are translocations.

Key words: FISH, X-ray worker, chromosome aberration, lymphocyte