The relationship of obesity and physical fitness (VO2max) to cardiopulmonary and metabolic function was examined in 132 healthy obese, nonsmoking men age 45-79. Obese men with higher VO2max had lower % body fat and waist-to-hip ratio (WHR) than obese men with low VO2max. The obese subjects with high WHR (upper body fat distribution) had higher systolic blood pressure, hyperinsulinemia and impaired glucose tolerance, lower high density lipoprotein cholesterol (HDL-C), and higher triglyceride (TG). VO2max (ml/kg FFM.min) was lower in the older men (r = -0.54, p less than .001), and 32% of the variation was accounted for by age and the one-second forced expiratory volume. Although pulmonary function was normal, 50% of the variability was predicted by age, height, and VO2max or WHR. Glucose tolerance and insulin correlated better with VO2max and indices of body composition than with age, while plasma TG and HDL-C correlated with body composition, not VO2max or age. Thus, while age affects the cardiopulmonary and metabolic function of obese older men, physical inactivity, obesity, and an abdominal body fat distribution (increased WHR) contributed significantly to their reductions in physiological function.