The aim of this study is to establish relationship between incidence of chromosomal aberrations and micronuclei in circulating human lymphocytes after fractionated irradiation in vitro. Blood samples (of males of mean age 32, range 30-34) were irradiated using X-rays (300 kVp, 10 mA, 2.7 ㎜ CuHVT) employing radiation doses of 1-4 Gy (dose-rate 1 Gy/min). Each dose was given in two equal fractions with four different time intervals between two irradiations: 30 minutes, 1 hour, 2 and 3 hours. Acute irradiated samples serve as positive controls. For each experimental point parallel cultures were set up: for chromosome aberration and micronuclei analysis. The results obtained in present study have shown that the best correlation was found between dicentrics and total chromosome aberrations versus micronuclei in all employed doses. In contrast to samples acutely irradiated where chromatid aberrations were no found, they are observed in all samples where radiation dose was delivered with the longest pause between two fractions (3 hours). Incidence of chromosomal aberrations decline faster than micronuclei at all given doses if the time interval between two irradiations is longer than 2 hours. The study highlighted that micronuclei is reliable parameter of the DNA damage in conditions of fractionated irradiation, that could be particularly important for estimation of radiosensitivity and recovery time of lymphocytes for patients undergoing radiotherapy.