OBJECTIVE To assess the effect of workplace-oriented dietary intervention on serum lipids. METHODS A cohort study. Screening for blood lipids and subsequent dietary intervention performed at a ferro-alloy factory where all the workers have at least one meal per working day served by the factory kitchen. METHODS Employees at Grundartangi ferro-alloy factory, Iceland. METHODS From 1 June 1989 to 1 June 1991, 155 workers participated in the screening and prevention programme. METHODS Changing the food served by the kitchen to 200 workers by lowering the total number of calories and increasing the content of fibre and unsaturated fats in the diet. RESULTS The mean serum cholesterol was lowered from 6.64 to 6.09 mmol/l or by -8.28% for the whole group (p < 0.001) after two years of intervention. In the subgroups studied, serum high density lipoprotein (HDL) increased (p < 0.001), whereas serum low density lipoprotein (LDL) decreased. Cholesterol/HDL and LDL/HDL ratios were reduced. General dietary habits seemed to change in a favourable way. No significant change occurred in body mass index or smoking habits, and there was little effect on exercise habits. CONCLUSIONS Workplace dietary intervention seems to be effective in reducing cardiovascular risk factors. Information provided to the kitchen staff is of importance, as well as information given to the employees, in order to obtain beneficial results from dietary change.