This study aims to assess and compare the aerobic fitness (max VO2) of 210 healthy adult men in sedentary occupations in Singapore. All the subjects studied were in codes 0 to 2 of the Singapore Standard Occupational Classification, comprising professional, technical, administrative and related workers. Their max VO2 were determined from direct analyses of their expired respiratory gases during an all-out run on a treadmill. Of these 210 men, 71 (33.8 per cent) were recreation-related regular exercisers and their mean max VO2 of 40.9 ml/kg per min STPD (at standard temperature and pressure, dry) and 95 per cent confidence interval of 39.2-42.6 ml/kg per min was significantly higher (p less than 0.001) than that of the remaining 139 men (34.3 ml/kg per min STPD) with 95 per cent confidence intervals of 33.2-35.4 ml/kg per min who were not regular exercisers. The regular exercisers also met the max VO2 requirements for heavy physical work capacity and compared favourably with the recommended standards for aerobic fitness in the National Physical Fitness Award of Singapore as well as Cooper's Standards based on North American men while the non-regular exercisers did not. The study has shown that the recreation-related regular exercise of the study-defined type, intensity, duration and frequency can significantly improve the physical work capacity of healthy adult men in sedentary occupations in Singapore.