Since 1984, coronary heart disease (CHD) risk factors have been prospectively assessed among Cincinnati firefighters free of CHD at study entry. In total, 806 firemen with a mean age of 37 years at entry have been followed for 6.4 years on average, contributing 5,173 person-years. CHD risk factors were measured every 1-4 years and included weight, blood pressure, cigarette use, fasting glucose, and lipid profile. When, in aggregate, these CHD risk factors were found to be in a high risk range, suggestions were made serially to reduce CHD risk. A composite high CHD risk factor score led to an exercise electrocardiogram (ECG) with thallium scan, which was repeated every 1-4 years. Myocardial infarction (MI) occurred in 7 men, with 1.35 MIs/1,000 man-years; 15 others developed CHD, with 4.25 MI + CHD/1,000 man-years. The firefighters' MI event rate (1.35 MIs/1,000 man-years) was lower (but not significantly, p > 0.1) than that for employed 30- to 39-year-old men free of CHD at entry (2.07/1,000 man years), who had an average follow-up of 5.4 years in the NHANES I study. At study entry, the 22 men who later developed CHD (vs. the 784 who did not develop CHD) were older (p = .0001), smoked more (p = .0001), and were more likely to have first degree relatives with CHD before age 60 (p = .017). After covariance adjusting for age, race, and Quetelet index, men with CHD (vs. those CHD free) had higher systolic and diastolic blood pressures (p = .0001, .0001), higher LDL cholesterol (p = .04), higher total cholesterol (p = .014), and higher triglycerides (p = .03). By Poisson regression, significant independent predictors of CHD events were age (p = .0007), cigarette smoking (p = .001), diastolic blood pressure (p = .056), and family history of CHD at age < or = 60 (p = .048). Men who later developed CHD and those without CHD did not differ by history of smoke inhalation (p > 0.3). The calculated ratio of savings to cost attributable to the program per year was 5.9/1 ($258,500/$43,600). In the current study, firefighting as an occupation was not associated with increased CHD event rates. CHD events that did develop were, for the most part, associated with modifiable CHD risk factors.