Purpose: Damage to vascular endothelial cells is a well recognised complication of the irradiation. Our objective was to determine the gamma-irradiation effect on the rat circulating endothelial cells (CEC). Material and methods: Eight-week old rats were divided into four groups: group 1 - rats were exposed to acute whole- -body gamma irradiation with a wide range of single doses (0.5, 1, 2, 4 and 8 Gy), group 2 - rats were exposed to fractionated low doses of irradiation (0.1, 0.5 and 1 Gy) every three days for two months, group 3 as group 2, but followed by two months of rest, group 4 were control animals. CEC (CD146 positive cells) in group 1 were counted following CD146-based immuno-magnetic separation after one day and one week, as well as at the end of experiment in the other groups. Results: Quantified CEC showed that there was a dose-dependent reduction in CEC count in group 1 (one week after irradiation) and group 2. A partial re-population of CEC was observed at the end of experiment in both group 1 and group 2 compared to control group. Group 3 showed a significant increase in CEC levels as compared with group 2 without reaching the control level. Conclusion: The number of CEC (CD146 positive cells) in rats exposed to whole-body gamma irradiation was reduced in a dose-dependent manner and it partly recovered during the two-month interval after irradiation. We suggest that CEC count may be an indicator of the radiation-induced vascular damage.