Shock waves were measured during walking on a treadmill on the metal tube of a below-knee KBM prosthesis, provided either with a SACH foot or with a Multiflex foot. Accelerations were measured in the axial direction and the dorso-ventral direction, about 160 mm proximal to the sole of the shoe. The accelerations had comparable amplitudes to those measured on normal legs. Dorso-ventral amplitudes (order of magnitude 4 g) were generally higher than the axial amplitudes. For some patients, the SACH foot gave much higher axial accelerations than the Multitlex foot did. In the dorso-ventral direction, the SACH foot showed a moderate resonance phenomenon in the autospectral density function in the range of 40-50 Hz. The Multiflex foot showed a more variable behaviour. For both types of feet, components above 65 Hz were negligible.