The dependence on the 5 0 nearest-neighbor nucleotide of effects from substituting U L for U M was studied in duplexes of the form, neighbor that is preceded by A M and U M , respectively. In both cases, the LNA substitution enhances duplex stability by 1.14 kcal/mol at 37 C. Thus, for seven duplexes, the enhanced stability from an LNA substitution is relatively independent of the nearest-neighbor nucleotide 5 0 to the LNA. The one exception is for the nearest neighbor 5 0 G M U L /3 0 r(CA). Interestingly, this nearest-neighbor combination is also destabilized by LNA substitution at a 3 0 terminal U (Table 1) . Evidently, an LNA substitution in the middle of a 2 0 -O-methyl strand usually affects heteroduplex stability with an RNA strand by about the same amount as an LNA substitution at a 3 0 terminus.