The amino acid compositions of soluble tryptic and chymotryptic peptides of the gamma chain of chimpanzee foetal haemoglobin have been determined. The peptides, accounting for all 146 residues of the gamma chain, were found to be identical in composition to the corresponding human gamma chain peptides. As in man, position gamma 136 can be occupied by glycine (G gamma chain) as well as alanine (A gamma chain). The ratio of G gamma to A gamma chains in the infant chimpanzee is approx. 2:1, and in the adult approx. 1:2.