Walking is most efficient when the least energy is spent over a certain distance. In six normal male subjects and 11 males with above-knee amputation the comfortable self-selected walking speeds and the most metabolically efficient walking speeds were determined. For that purpose energy expenditure was measured per second and per meter at six incremental walking speeds. Heart and step rate were registrated also at each walking speed. The results showed that in subjects who have not undergone amputation the comfortable walking speed is the same as the most efficient walking speed. However, in the above-knee amputee group, the comfortable walking speed is lower than the most efficient walking speed. When both groups walked at their own efficient walking speed they had the same energy expenditure per second.