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. 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 16 kDa (15)N, (13)C-labeled non-deuterated apo-CcmE and a 48 kDa uniformly (15)N, (13)C-labeled and fractionally ( approximately 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.