The measurement of ground reaction forces is important in the biomechanical analysis of gait and other motor activities. It is the purpose of this study to show the feasibility of ambulatory measurement of ground reaction forces using two six degrees of freedom sensors mounted under the shoe. One sensor was mounted under the heel, the other under the forefoot, thus allowing normal gait with flexion of the foot during push-off. The measurement of the ground reaction force was evaluated in a healthy subject, who walked repeatedly over a force plate. The ground reaction force reconstructed from the instrumented shoe sensor signals corresponded well with the force plate measurements, the RMS difference between the moduli of both ground reaction force measurements was 18.4 /spl plusmn/ 3.1 N (2.3 /spl plusmn/ 0.4% of maximal vertical ground reaction force) over 12 evaluated trials. The RMS distance of the center of pressure estimates of both measurement systems after optimal alignment was 3.1 /spl plusmn/ 0.4 mm.