Solution-phase measurements and ab initio quantum-mechanical calculations (MP2/6-311G**//MP2/6-31G*) of the dipole moments of 4-nitropyridine N-oxide (µexptl = 0.83 ± 0.04 D, µcalc = 0.97 D) and 3-methyl-4-nitropyridine N-oxide (µexptl = 0.69 ± 0.05 D, µcalc = 0.89 D) show that the electronic effects of methyl substitution are localized and much smaller (Δµ < 0.2 D) than had previously been thought.