The novel deoxyribonucleotide α-[d(CpCpTpTpCpC)] and its complement β-[d(GpGpApApGpG)] were synthesized by the phosphotriester method. 1H-NMR-NOE examination of the α-hexamer revealed that the cytosine and thymine bases appear to adopt anti conformations in this strand. In addition the deoxyribose of the thymidine moieties may adopt average conformations approximating to C3'-endo while the cytidine furanose groups are close to C2'- endo conformations. Both hyperchromicity in thermal melting and detection of base paired imino protons in 1H-NMR studies in H2O provide evidence for the annealing of α-d[CCTTCC] with its complement β-d[GGAAGG] in potassium phosphate buffer pH 7.1 containing 10 mM magnesium chloride. Under these conditions thermal melting begins at 38°C and its complete at 45°C. NOE experiments do not permit a decision on the polarity of annealing (predicted to be parallel) for this particular pair of sequences.