We conducted this study to examine the relationship between shift work duration and the metabolic risk factors of cardiovascular disease among shift workers. The study population consisted of 226 female hospital nurses and 134 male workers at a firm manufacturing diapers and feminine hygiene materials, whose mean ages were 28.5 yr for the nurses and 29.1 yr for the male workers. The fasting blood sugar level, serum cholesterol, blood pressure, height and weight, waist and hip circumferences (only for the nurses), and numbers of walks during work (as a measure of physical activity) were measured. Using the Karasek's job contents questionnaire, job stress was assessed. Information about the years of work, shift work duration, past medical and behavioral history, including smoking, was obtained by a self-administered questionnaire. With definitions of hypertension as systolic blood pressure (SBP) > or =160 or diastolic blood pressure (DBP) > or =90 mmHg occurring at least once, hypercholesterolemia as serum total cholesterol > or =240 mg/dl, obesity as body mass index (BMI) > or =25 kg/m(2) and as waist to hip ratio (WHR) > or =0.85, we examined the prevalences of metabolic risk factors among subjects. Regression analyses to show the relationships between shift work duration and metabolic risk factors were performed using simple and multivariate models stratified by age, and adjusted for smoking, drinking, job strain and physical activity. Duration of shift work was significantly associated with SBP or cholesterol level among male workers aged 30 or more. Among female nurses, it was inversely associated with DBP (in those who were below 30 yr old) and cholesterol (in those who were aged 30 or more). BMI was non-significantly associated with the duration of shift work in both male workers and female nurses who were 30 yr old or more. WHR in female nurses increased slightly according to increasing duration of shift work. Fasting blood sugar was not significantly associated with the duration of shift work in either sex regardless of age-group. These results suggest an association between shift work duration and the metabolic risk factors of cardiovascular disease.