A complete assignment of the1H and13C NMR spectra of four 6(9)-methylbenzo[b]naphthyridines in CDCl3is presented. The proton signals have been assigned from (1H-1H) coupling patterns and by the comparisons of chemical shifts with those of related heterocycles. Complete13C assignments have been made using proton detected one bond (13C-1H) 2D heteronuclear single quantum correlation, the INEPT technique, and chemical shift comparisons with related heterocycles. The proton detected long range (13C-1H) 2D heteronuclear multiple quantum correlation experiment leads to an unambiguous assignment of the two quaternary carbons in 6-methyl-benzo [b][1,5] naphthyridine.