The objective of the study was to evaluate the contribution of dietary factors to variation of plasma levels of lipids, apoproteins and lipoparticles in the Northern Ireland population. This study was part of a larger case-control study of the genetic and environmental determinants of myocardial infarction in France and Northern Ireland. A random sample of 175 middle aged men was drawn from the population covered by the Belfast MONICA project register. Habitual diet was assessed by a questionnaire. A blood sample was obtained after an over-night fast for determination of plasma levels of lipids, apoproteins and lipoparticles. All participants had a medical examination and completed a lifestyle questionnaire. In a stepwise regression, after adjusting for co-factors (i) vitamin C and (ii) alcohol consumption were the only nutrients which contributed significantly to the variation in, respectively, (i) Total Cholesterol, LDL Cholesterol and Apolipoprotein B (inverse correlation) and (ii) HDL Cholesterol and LpAI (positive correlation). The amount of variation explained by the final models was modest, ranging from 4% to 15%. In conclusion, in this Northern Ireland population, habitual diet contributes to little of the variation in plasma levels of lipids, apoproteins and lipoparticles.