The title compound was synthesised for use in an investigation of the antigenicity of polypeptides with a known sequence of amino-acids. Polymerisation of O-t-butyl-L-tyrosyl-γ-t-butyl-L-glutamyl-L-valylglycine Pentachlorophenyl ester hydrochloride on the partially blocked monomer [1-¹⁴C]glycine ethyl ester hydrochloride gave poly-(O-t-butyl-L-tyrosyl-γ-t-butyl-L-glutamyl-L-valylglycyl)[1-¹⁴C]glycine ethyl ester. The t-butyl groups were then removed. The molecular weight, determined by both gel filtration and radioassay, was > 1 × 10⁵.