In a 7-year follow-up of 11,121 Yugoslav men first examined in 1964-1965 when they were 35-62 years old, it was found that the incidence of coronary heart disease (CHD) was one-fourth that of a comparable Framingham (USA) group. Incidence in rural men was only 59% of urban men. In both urban and rural groups, men with higher blood pressures had greater CHD incidence, and cigarette smoking was also associated with greater incidence. In the urban but not the rural groups serum cholesterol and weight/height were also CHD risk factors. Levels of serum cholesterol and weight were lower in urban Yugoslavia than Framingham and lowest in rural Yugoslavia. At the same levels of these characteristics Framingham incidence was 3 times that in Yugoslavia. At the very low rural levels of weight and blood pressure CHD incidence was the same in urban as rural Yugoslav groups.