ANALOGUES of purines and pyrimidines have been used as antimetabolites1. Some of these have been converted into their nucleosides or nucleotides which also act as antimetabolites2. Analogues of nucleosides in which D-ribose or 2-deoxy-D-ribose is replaced by another carbohydrate or carbohydrate analogue have also been extensively studied2. Some of the nucleotide analogues have been converted into polynucleotide analogues by the use of suitable enzymes3–6 and by taking advantage of the fact that certain micro-organisms will incorporate the nucleotide analogue into DNA or RNA (refs. 7–13). The synthesis of polynucleotide analogues in which the purine or pyrimidine side chains are linked by a type of backbone different from the sugar phosphate backbone of the natural polynucleotides has been reported in previous work from this laboratory. One type was obtained by copolymerizing 5′-O-acrylyluridine with acrylamide14 and another by reacting adenosine dialdehyde with polyacrylic acid hydrazide15. Both these polymers contained a fraction which hybridized with denatured DNA trapped in agar and with denatured DNA in solution.