Polynucleotide templates containing C (cytidine) as the major component facilitate the synthesis of oligonucleotides from mixtures of the activated mononucleotide derivatives (as indicated by structure 1 in the text). A nucleotide is incorporated into oligomeric products if and only if its complement is present in the template. The reaction has a high fidelity and produces products with mean chain lengths of six to ten nucleotides. Bases other than guanosine are incorporated within oligomers or at their 3' termini, but rarely at their 5' termini.