199Hg NMR spectra are reported for the complexes [MeHgL]NO3 containing either two- (e.g. L = pyridine) or three-coordinate mercury (e.g. L = 2,2'-bipyridyl). For unidentate and bidentate ligands of similar basicity chelation with bidentate ligands to give three-coordinate mercury results in upfield shifts of 199Hg resonances from that of the linear complexes. For complexes of unidentate ligands shifts correlate with changes in base strength of the ligands, and methyl substitution in the 2 position of pyridine appears to result in an upfield shift of ca. 30 ppm. Effects of substitution in the 2 position are very strong in complexes of unidentate 2-benzylpyridine and 3,3'-dimethyl-2,2'-bipyridyl. Comparison of the 199Hg shifts with J(1H-199Hg) shows the coupling constant to be insensitive to substitution in the 2 position in linear complexes and is a function only of the ligand base strength.