The entire cohort of 3,403 firefighers is followed up to 1996 in this longitudinal study. The investigators are using a variety of tracing sources, including the National Death Index, and obtaining death certificates to determine date and cause of death. Cohort data will be analyzed to address the following aims: (1) To provide a longitudinal description of and determine the interrelationships among physical fitness, physical activity, and other measured risk factors; (2) to determine whether levels of physical fitness are related, independently of other known and measured risk factors, CHD and all-cause mortality; (3) To determine whether there is a gradient of decreasing CHD risk with increasing levels of physical fitness, or whether there appears to be some threshold of physical fitness, above which CHD risk stabilizes; (4) To determine whether the relationship between physical fitness and CHD and all-cause mortality varies by such cardiovascular risk factors as age, cholesterol levels, blood pressure, smoking, and obesity.