Increased levels of serum triglycerides in shift workers have been reported in two population-based studies. In order to examine this relationship and to take some common confounding factors into account this cross-sectional study of 562 shift and day workers was carried out. The shift workers had significantly higher levels of serum triglycerides. gamma-glutamyltransferase and total cholesterol, and Body Mass Index did not differ between the groups. The cause of increased serum concentrations of triglycerides is unclear. The present study provides no evidence to support the assumption that alcohol drinking or obesity accounts for increased levels of serum triglycerides in shift workers.