Sister chromatid exchange(SCE) has recently become a common cytogenic assay system for detecting exposure to chemical mutagens and carcinogens. One application of SCE is the monitoring of populations believed to be exposed to such agents. A cross-sectional study of SCE frequency in peripheral blood lymphocytes from 40 college students aged 18 to 26 years was conducted. The effects of cigarette smoking alcohol and coffee consumption, dietary and environmental factors on SCE were assessed. A mean spontaneous SCE per cell for the smokers(4.88$pm$0.17). The SCE levels of the smokers were associated with the personal smoking amount ; the observed increase in the SCE frequency correlated with the number of cigarettes smoked per day (P<0.05). There was no effect of age on SCE. There were positive linear relationship between SCE and food frequency score of meat and fish group (P<0.05) or instant food group(P<0.01) in non-smokers. But in smokers, a significant inverse association between SCE and food frequency score of green and yellow vegetable group(P<0.05). Alcohol intake produced a significant increase(P<0.01) of SCE in comparison with the mean SCE for those not drinking alcohol in combine subjects. Other dietary parameters, including coffee intake, use of artificial sweetners and processed foods, did not show any increase in SCE. SCEs were inversely related to blood glucose and serum cholesterol levels of the combine subjects. No significant correlations were found between SCE frequencise and any other hematological parameters of the subjects.