H-phosphonate internucleotidiclinkages and unmodified nucleobases were synthesized for the first time by the new H-phosphonate method using N-unprotected monomers. The 6-hydroxyhexyl phosphonates at both the 5′ and 3′ ends were found to be highly effective for stabilization of the H-phosphonate oligonucleotides. Solid-phase synthesis of H-phosphonate oligodeoxy-ribonucleotides containing dA, dC, dG,