The 14-mer oligodeoxynucleotide d(C3GC3GC3GC2) acts as a template to facilitate the cooligomerization of guanosine 5'-phospho-2-methylimidazolide and cytidine 5'-phospho-2-methylimidazolide. The predominant products are a series of 3'-5'-linked oligonucleotides, complementary to the template, ranging in length from GGC to GGCGGGCGGGCGGG. Thus simple, non-enzymatic template-directed reactions can result in the accurate transfer of substantial amounts of information from template to products. The 15-mer oligodeoxynucleotide d(C3GC3GC3GC3) is also an efficient template, but directs the synthesis of the same family of products that are formed on the 14-mer template. This unexpected finding is explained by the preferential conversion of the dimer GG to GGC rather than to GGG. These results are interesting in the context of molecular evolution. They suggest that the detailed kinetics of template-directed synthesis could form the basis for the selection of one replicating oligonucleotide from a family of closely related oligonucleotides.