Oxygen consumption (VO2), heart rate, body temperature, and stride frequency were measured in Marabou storks walking on a treadmill at a range of speeds and gradients. VO2 was linearly related to speed at gradients up to 11 degrees and speeds up to 1.4 m . s-1, and the slope of the VO2/speed regression increased with the treadmill angle up to 9 degrees. At 11 degrees there was a fall in the slope. Analysis indicates the cost of horizontal movement of about 1.1 ml O2 . m-1 (mean wt 4.5 kg). The cost of vertical movement is 7.13 ml O2 . m-1 and the efficiency about 30%. Maximum recorded VO2 was about five times resting, and there was no indication of an oxygen debt at any value for VO2. Heart rate was directly proportional to vO2 over the range studied, and at high heart rates successive cardiac cycles overlapped. Body temperature did not change significantly during exercise. Stride frequency was linearly related to walking speed but with a nonzero intercept so that stride length changed with speed, but there was no observed change in gait with speed. These data are discussed in comparison with published scaling equations and with data from mammals.