OBJECTIVE To assess the relationship of biological markers of dietary factors with blood pressure (BP) (Core Study) and with age-adjusted mortality rates of stroke and ischemic heart disease (Complete Study) in the WHO Cardiovascular Diseases and Alimentary Comparison (CARDIAC) Study, a multicentre epidemiological study in 55 centres of 24 countries as of 1993. METHODS From each population, 100 men and 100 women aged 48 to 56 years were randomly selected for BP measurement, 24-hour urine collection, blood tests, etc. Various biological dietary markers from the urine and blood were analysed centrally. Age-adjusted mortality rates from stroke and ischemic heart disease were obtained from 19 centres in 14 countries. RESULTS Core Study: Cross-centre analyses, using simple linear regression, showed a positive relationship of body mass index to systolic BP and diastolic BP in men (p < 0.001) and women (p < 0.05). There were also strong positive correlations between 24-hour sodium excretion rates and both systolic and diastolic BP (both p < 0.01) in men. An inverse relationship was found between the 24-hour magnesium/creatinine excretion ratio and diastolic BP (p < 0.05) in men. Complete Study: Stroke mortality was significantly positively related to the 24-hour sodium excretion rate in men (p < 0.01) and to the sodium/potassium ratio in both sexes (p < 0.05). It showed an inverse relationship of serum phospholipid with serum total cholesterol (p < 0.05) and a positive relationship with arachidonic acid. A strong positive relationship between serum cholesterol level and ischemic heart disease (p < 0.001) was observed in men. The serum phospholipid n-3 polyunsaturated fatty acid (PUFA) level and the PUFA to saturated fatty acid (SFA) ratio were significantly inversely correlated with ischemic heart disease. The 24-hour taurine excretion rate, a biological marker of seafood protein intake, showed a significant inverse correlation with ischemic heart disease in both sexes (p < 0.01). CONCLUSIONS The Core Study revealed a consistent adverse effect of high body mass index and excess salt intake on BP and a beneficial effect of magnesium on BP. The Complete Study demonstrated an adverse effect of high sodium, low potassium intake and hypercholesterolemia on stroke; and an adverse effect of cholesterolemia as well as beneficial effects of serum phospholipid n-3 PUFA, PUFA/SFA and the taurine excretion rate on death from ischemic heart disease.