The 1H NMR spectrum of 113Cd6 Scylla serrata metallothionein isoform 1 (MT-1) is presented and analyzed in considerable detail by using two-dimensional chemical shift correlated (COSY) methods. Using these methods, it has been possible to associate most 1H resonances with amino acid type. The 1H chemical shifts for all 18 cysteine residues present in the protein have been identified, as has the range of heteronuclear 1H-113Cd scalar coupling between the 113Cd ions and the cysteine β-CH2 protons, 10 Hz < 3J113Cd-1H < 65 Hz. The relationship of these 1H NMR data to the proposed cluster structures derived from 113Cd NMR is discussed with some emphasis being placed on the identification of bridging cysteine residues, required by the proposed cluster structures, via the analysis of the heteronuclear scalar coupling present in the cysteine αβ cross-peaks in the 1H COSY spectrum. It is concluded that, in the absence of a calibrated Karplus equation for 3J113Cd-1H and in the presence of short 113Cd T1 values, identification of the 1H resonances arising from bridging cysteine residues using heteronuclear scalar coupling data alone is not readily achievable.