By adding various substrates such as glucose, lactate, pyruvate, aspartate, malate, and alanine to both acatalasemia patients and the normal, the fluctuation of the pyruvic acid contents accompanying the respiration of erythrocytes had been investigated, but no difference of the contents could be observed between the two groups. Thus it has now become clear that even in these patients the pyruvic acid in erythrocytes, in so far as the respiration of erythrocytes, takes hardly any acitve part in the disposal of H(2)O(2)supposedly to be liberated during respiration.