In this study the suitability of fluorescence in situ hybridization (FISH) for dicentric detection using a commercially available alpha-satellite probe (Oncor) to label centromeres was compared with the conventional technique for the detection of unstable aberrations. A standard FISH protocol was applied for centromere labelling. Dose-response curves using blood samples irradiated in vitro with gamma-rays (60Co) at a dose-rate of 0.1 Gy/min were established using both techniques and compared. No statistical difference was observed between either method. The FISH technique thus allows a correct detection of unstable aberrations when an alpha-satellite DNA probe is used.