We propose the use of 13 C-detected 3D HCC–TOCSY experiments for assignment of 1 H and 13 C resonances in protonated and partially deuterated proteins. The experiments extend 2D C-13-start and C-13-observe TOCSY type experiments proposed earlier [J. Biomol. NMR 26 (2) (2003) 167]. Introduction of the third 1 H dimension to 2D TOCSY: (i) reduces the peak overlap and (ii) increases the sensitivity per unit time, even for highly deuterated (>85%) protein samples, which makes this improved method an attractive tool for the side-chain H and C assignment of average sized proteins with natural isotope abundance as well as large partially deuterated proteins. The experiments are demonstrated with a 16kDa 15 N, 13 C-labeled non-deuterated apo-CcmE and a 48kDa uniformly 15 N, 13 C-labeled and fractionally (∼90%) deuterated dimeric sFkpA. It is predicted that this method should be suitable for the assignment of methyl 13 C and 1 H chemical shifts of methyl protonated, highly deuterated and 13 C-labeled proteins with even higher molecular weight.