Abstract Novel flexible oligodeoxynucleotides containing ( S)-1-(2,3-dihydroxypropyl)thymine or 2′,3′- seco-thymidine nucleoside analogues were synthesized on an automated DNA-synthesizer. Oligodeoxynucleotides with one, two or three acyclic nucleosides incorporated in the middle or in the ends of 17-mers have been evaluated. 3′-End-modified oligomers were significantly stabilized towards 3′-exonucleolytic degradation compared to unmodified analogues and showed acceptable hybridization properties as measured by UV experiments. For oligodeoxynucleotide analogues containing the three novel acyclic monomers in the middle, a more pronounced reduction in duplex stability was observed. All oligodeoxynucleotides containing acyclic nucleoside analogues made so far are evaluated with respect to stability towards 3′-exonucleolytic degradation and hybridization properties.