< Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn, a proposed serum thymic factor, was synthesized. The protected precursor, < Glu-Ala-Lys(i-Noc)-Ser(Bzl)-Gln-Gly-Gly-Ser(Bzl)-Asn, was prepared by a combination of solid phase and solution methods. The benzyl blocking groups were removed by HF and the i-Noc blocking group was removed by catalytic hydrogenation.