A single vessel cyclic synthesis process for preparation of a sialyl.alpha.2.fwdarw.3.beta.galactoside is disclosed. In accordance with this process, a sialyltransferase acceptor is sialylated in an aqueous reaction medium by an .alpha.(2,3)sialyl transferase and CMP-sialic acid to form a sialyl donor substrate and CMP. In the presence of the trans-sialidase of Trypanosoma crusi, that sialyl donor substrate provides a sialyl group for a trans-sialidase acceptor, thereby preparing the sialyl.alpha.2.fwdarw.3.beta.galactoside. The .alpha.(2,3)sialyltransferase acceptor is reformed upon trans-sialidation of the latter acceptor, and the sialyl donor substrate is reformed using the .alpha.(2,3)sialyltransferase and a CMP-sialic acid recycling system that combines CMP with sialic acid that is also present in the vessel. The K.sub.m /V.sub.max value for the .alpha.(2,3)sialyltransferase acceptor is less than one-tenth the value of K.sub.m /V.sub.max of the trans-sialidase acceptor for the .alpha.(2,3)sialyltransferase.