An investigation of effects of shift work on cardiovascular risk factors has been carried out on workers of a motor company in Ulsan, for 2 months from 20 April to 20 June,1993. This cross-sectional survey was designed to compare the shift workers (n=420) with day workers (n=88). The study subjects were drawn from workers who were employed in twelve hour shift system. A control group who never experienced shift work was drawn from different sections of the factory. Each worker completed a medical and occupational questionnaire and cardiovascular risk factors such as blood pressure, total cholesterol, triglyceride, apolipoprotein A-1 and B were measured. In univariate analysis, apolipoprotein B and the ratio of apolipoprotein B to apolipoprotem A-1 increased in shift workers. In multiple regression analysis for the systolic blood pressure, shift work was significant independent variable (p=0.059). In multiple regression analysis for the cholesterol, age and body mass index were significant independent variables(p<0.01), but shift work was not a statistically significant independent variable. In multiple regression analysis for the ratio of apolipoprotein B to apolipoprotein A-1, shift work was significant independent variable (p<0.05). Shift workers who have engaged in shift work more than 5 years have an excess of total cholesterol, apolipoprotein B and ratio of apolipoprotein B to apolipoprotein A-1 than those who have engaged in shift work less than 5 years (p<0.05). In multiple regression analysis for the cholesterol, duration of shift work was a significant independent variable (p=0.012). In multiple regression analysis for the apolipoprotein B and ratio of apolipoprotein B to apolipoprotein A-1, duration of shift work was not a significant independent variable.