Compound muscle action potentials of the extensor digitorum brevis were obtained in two groups of normal and uraemic subjects by stimulating the deep peroneal nerve at the ankle and at the capitulum fibulae. Particular attention was drawn to the index of desynchronisation supplied by the amplitude change in the muscle potential evoked by distal and proximal stimulation of the same nerve. Statistical studied confirmed the soundness of this index in the normal and in the pathological condition, and showed a significant increase of the values found in uraemic patients. The complex of the data pointed out the advantage of integrating the usual motor conduction velocity determination with the mentioned desynchronisation index.