A number of studies have shown total leukocyte count to be a risk factor for ischemic heart disease, but there is little information on the role of the individual types of leukocyte, and the role of smoking is controversial. The Caerphilly and Speedwell studies recruited 4,860 men aged 45-63 years between 1979 and 1983 in South Wales and the West of England, respectively. At the 10-year follow-up, the total leukocyte count predicted ischemic heart disease events after adjusting for the classical risk factors, including smoking. Five-year follow-up results were available for differential white cell counts. The main contributor to the increase in total count in the men who developed disease was the neutrophil count. There was also a statistically significant increase in the eosinophil count.