Cook, Heilbron and Levy1 have recently prepared tetraglycylglycine and several di-peptides by reaction of 2-thio-5-thiazolones with amino-acid derivatives. During the past few years, much interest has also been shown in the polymerization potentialities of the N-carboxy anhydrides of α-amino-acids2–5. Study of the reaction of these anhydrides with simple organic bases has now indicated the mechanism of their polymerization and provided a new method of building up polypeptides by addition of single amino-acid units.