Alpha-beta chimeric 17-mer oligodeoxyribonucleotides containing either 5, 10 or 15 beta nucleotides were synthesized, The stability of the RNA/chimera hybrids was only slightly affected by the alpha stretch and by the alpha-beta link, as was the affinity of the Moloney Murine Leukemia Virus reverse transcriptase for the duplexes, All chimeras inhibited in vitro cDNA synthesis in a cell-free system to various extent, via the degradation of the RNA target by RNase H.