The purpose of this study was to evaluate the cardiopulmonary function and body composition of sedentary and highly active paraplegics. Four age-matched groups of men (n = 41) were studied: wheelchair-bound sedentary (WS), wheelchair-bound athletes of international caliber (WA), able-bodied sedentary (NS), and able-bodied athletes of national Israeli teams (NA). Although of similar height, WS were significantly (p less than .05) heavier and more obese (skinfolds) than WA and NS. Maximal oxygen consumption (VO2max arm), as measured during arm ergometry by direct open circuit spirometry, was significantly lower in WS (19.58 plus or minus 5.53 ml/kg per min) than in WA (35.00 plus or minus 7.55). The latter had significantly higher VO2max arm than did NS (25.79 plus or minus 3.98). However, no significant difference was observed between WA and NA (38.05 plus or minus 6.25). A similar trend, favoring WA over WS, was shown for maximal minute ventilation and maximal oxygen pulse. Functional lung volumes (FVC, FEV1.0, MBC) did not differ significantly between WA and WS. Heart rates at submaximal work loads were higher in WA than in NA, but markedly lower than in WS. Clear-cut conclusions can be obtained only by a longitudinal study, but these data suggest a marked decrement in cardiopulmonary functions, related to the oxygen transport system, in men whose lower limbs have been immobilized for years. A reversed trend is shown for paraplegics who regularly activate their upper limbs and trunk muscles.