Activated derivatives of purine-containing deoxynucleosidedimonophosphates spontaneously oligomerize to produce pyrophosphatelinked oligonucleotide analogues. These analogues are of potential interest as models of primitive, polynucleotide precursors. The efficiency of oligomerization (G and A much greater than I) appears to reflect a combination of stacking forces and the specific geometric orientations of the stacked units. Under favorable conditions, chain-lengths greater than 20 have been obtained for oligomers containing G in the absence of a template. In the presence of a complementary template, the activated derivatives of G and A oligomerize much more extensively. An acyclo-analogue of G (9-(l,3-dihydroxy-2propoxy)methylguanine) has also been shown to undergo template-directed oligomerization on poly(C). These observations suggest the possibility that information transfer might have evolved in chemically simpler systems and that this function was taken over by nucleic acids at a later stage in evolution.