A Kofranyi‐Michaelis respirometer has been used to measure net energy expenditures in 16 women and 52 men undergoing rehabilitation following hemiplegia. Measurements were made during seated rest, standing, comfortable ambulation, and ascent and descent of a laboratory staircase. Because tasks were performed more slowly than in the able‐bodied, all data were expressed as net oxygen cost (ml/[kg.m]) relative to seated rest. Resting metabolism was slightly reduced by hemiplegia (3.1±0.7 and 3.4±0.7 ml/[kg‐min] in men and women, respectively). Stair climbing was performed with a low net mechanical efficiency (6 to 8%). The metabolic cost of ambulation was also high relative to the able‐bodied individual, particularly at slow speeds of walking. Above a pace of 40 m/min in women and 50 m/min in men, the energy cost was only 10 to 20% higher in some hemiplegics than in the able‐bodied, but because of age and disability, many of the subjects with hemiplegia could not attain such speeds. We conclude that although some apparent optimization of the energy cost of ambulation is due to a consideration of the gross rather than the net oxygen cost, a combination of age and disability holds many individuals with hemiplegia to a walking speed that is mechanically inefficient.