THE large amount of free amino-acid which surrounds haemoglobin freshly released from red blood cells cannot be dialysed away from the protein even after vigorous washing (48 h, running water). The amino-acids still released after such washing may come from (a) metabolism of bacterial contaminants, (b) cellular enzymes, (c) amino-acids secondarily bonded to the protein, and (d) the cleavage of peptide bonds. It is impossible to rule out (a) and (b) in the case of haemoglobin.