Methods for making monodisperse polyester copolymers of predetermined length, composition, and sequence are reported. Alternating oligomers of (L)-lactic-co-glycolic acid (La-co-Gl), isosteric with polypeptides, are prepared by solution methods of protecting, coupling, and deprotecting alcohol and acid groups. The carboxylic acid is protected by benzyl ester formation and released by hydrogenation. The hydroxyl group is protected as the methoxyethoxyethyl ether and deprotected with sodium iodide and trimethylsilyl chloride. Coupling uses dicyclohexylcarbodiimide. End-capped alternating oligomers containing -(GlLa)(4)- and -(GlLa)(8)- show polymer properties. They are noncrystalline oils that exhibit discernable T-g. The conformation of -GlLa- and -LaGl- diads in the polyesters is shown to be similar to isosteric peptide diads -GlyAla- and -AlaGly-. Exactly structured, monodisperse polyesters suggest a chemical parallel to proteins. Designed structural templates combining sheet-form -(Gl)(n)- and helical -(La)(n)- segments are attractive synthesis targets. The solution preparations reported here can be applied, but it is suggested that biosynthetic methods for introducing single ester units into peptide chains be adapted to synthesize precisely fashioned polyesters.