The C-H activation of the methyl group of tetramethylthiourea by cis-[PtL(2)(NO(3))(2)] (L = phosphine or N-heterocyclic carbene) has been investigated as a function of the ligand L. The presence of an electron-withdrawing group on the tertiary phosphine was found to promote the process. Moreover, when an excess of nitrate anion is present in the reaction mixture, the rate of C-H bond activation is retarded, suggesting the key role of an unsaturated tri-coordinate Pt(II) species as intermediate.