The contribution of secular changes in the distribution of ischemic heart disease risk factors and medical care utilization to the decline in ischemic heart disease mortality was investigated using data collected on the nine-year ischemic heart disease mortality experience of two cohorts selected to be representative of Alameda County, California, in 1965 and 1974. With adjustment for age, sex, race, and baseline ischemic heart disease conditions and symptoms, there was a 45% decline in the nine-year odds of ischemic heart disease mortality between the two cohorts (1965/1974, odds ratio (OR) = 1.82, p = 0.0001). Further adjustment for cohort differences in the following ischemic heart disease risk factors did not explain the decline: smoking status, leisure-time physical activity, self-assessed physical activity, alcohol consumption, body mass index, or social network participation; neither did adjustment for measures of education, utilization of preventive medical care, availability of a regular physician or clinic, health insurance coverage, number of physician visits during the last 12 months, or occupation. There was no change in the estimated ischemic heart disease decline when all adjustment variables were included in a logistic model (1965/1974, OR = 1.81, p = 0.0002). These variables do not appear to explain the large decline in nine-year ischemic heart disease mortality between these two cohorts.