The authors compare the enantiomeric cross-inhibition of D- and L-guanosine 5'-phosphoro-2-methyl-imidazole (I) polymn. on C10 (RNA), dC10 (DNA), or hC10 (hexitol nucleic acid) (II). RNA or DNA templates catalyze efficient oligomerization of D-I, with a strong enantiomeric cross-inhibition by L-I, but II shows efficient oligomerization of D-I with a less sever cross-inhibition, resulting in G6-9 polymers, thus showing that efficient selection of one optical isomer from a racemic mixt. of nucleotides during nonenzymic oligo-nucleotide synthesis on an analog of a nucleic acid template is possible, which may be of relevance to prebiotic conditions. [on SciFinder (R)]