Coronary heart disease (CHD) mortality declined by approximately 23.5% in New Zealand men aged 35-64 years between 1968 and 1980. The contributions of secular trends in dietary fat and tobacco consumption to this decline were examined using data from national consumption statistics and population based studies of risk factor levels. Per capita saturated fat and dietary cholesterol consumption fell by approximately 12% and 10% respectively during this period while polyunsaturated fat consumption increased by 73%. Per capita tobacco consumption fell by approximately 15%. Using equations developed by Keys and Hegsted it was calculated that the mean serum cholesterol level declined by between 6.6 and 10.3 mg/dl (2.9%-4.4%) during this period. The potential impact of these risk factor changes on CHD mortality was estimated using a Framingham multivariate logistic risk function. Between 38% and 51% of the observed decline in CHD mortality in men aged 35-64 years in New Zealand between 1968 and 1980 could be accounted for by the calculated changes in serum cholesterol and tobacco consumption. If serum cholesterol and cigarette smoking were reduced further to meet current recommendations, it is estimated that CHD mortality would decline by a further 26%-30% from the 1980 level.