We measured the physiological energy expenditure that was associated with several modes of mobility in 151 individuals with paraplegia that resulted from spinal cord injury. The relationship of the neurological level of the spinal lesion, extent of paralysis, orthotic requirement, and type of gait pattern was evaluated. The patients who required a bilateral knee-ankle-foot orthosis in order to walk with a swing-through crutch-assisted gait had an average rate of oxygen consumption that was 43 per cent greater than that of the patients who used a wheelchair and 38 per cent greater than was required for normal walking. Their average walking speed was slow in comparison with wheelchair propulsion or normal walking. Furthermore, the paraplegics in whom the hip flexor and knee extensor muscles were intact bilaterally and who were able to walk with a reciprocal crutch-assisted gait, but did not require knee-ankle-foot orthoses, did no better. They had a rate of oxygen consumption that was 20 per cent greater than that required for wheelchair use and 15 per cent greater than that required for normal walking. In addition, their mean walking speed was the slowest of all of the groups. These findings account for the common clinical experience that most paraplegics who require a knee-foot-ankle orthosis bilaterally and use a swing-through crutch-assisted gait prefer to use a wheelchair, and discontinue walking as the primary means of mobilization after gait-training.(ABSTRACT TRUNCATED AT 250 WORDS)