OBJECTIVE: To study sister chromatid exchange (SCE) frequency in lymphocytes of pregnant women with intrauterine growth retardation (IUGR) infants. METHODS: The frequency of SCE in peripheral blood lymphocytes of 14 pregnant women with IUGR babies and 90 normal pregnant women as well as the umbilical blood of their infants were investigated. RESULTS: The mean frequency of SCE in maternal and umbilical blood with normal pregnancy were 7.58 +/- 0.32 and 5.05 +/- 0.29 respectively, while they were 10.53 +/- 2.69 and 7.25 +/- 1.34 in IUGR group respectively. The difference of SCE levels between the 2 groups of mother was statistically significant (P < 0.01), so was that of the umbilical blood group. CONCLUSION: One of the causes of IUGR may be related to heredity injury. Thus, SCE will be a new diagnostic index to predict IUGR.