Aerobic capacities of workers vary a great deal, as do the metabolic energy expenditure requirements of various manual jobs. This study was conducted to determine if the metabolic energy requirements on 11 jobs correlated with the aerobic capacities of 78 young male workers employed on the jobs. The results disclosed that the workers' mean aerobic capacities were correlated with the job energy requirements (r = .84), and that the average job metabolic rates were at approximately 35% of the estimated aerobic capacities of the workers. The jobs requiring a high energy expenditure rate (ie, those above 5.0 kcal/min-1) were associated with heart rates above 110 beats per minute averaged over eight hours. At this higher energy expenditure rate level, no age decrement in aerobic capacities was found, although a significant decrease was found with age in those employed in less demanding jobs.