Techniques for the biosynthetic incorporation of selenomethionine into biomolecules have recently been exploited to produce both heavy-atom derivatives and NMR probes for the elucidation of local and global structures of a variety of biological macromolecules. Since the work of Böck and co-workers in 1994, also chalcogen analogue replacement of cystine by selenocystine residues in proteins can be achieved to study structural, mechanistic and functional aspects of enzymes. This paper reports the 1 H and 77 Se NMR spectroscopic characterisation of l,lselenocystine with 77 Se at natural abundance and 92% enriched: υ 1 H , υ 77 Se ; 1 J 77 Se, 77 Se 0 , 2 J 1 H ˇ1,ˇ2 , 77 Se , 3 J 1 H ˇ1,ˇ2 , 77 Se 0 , 3 J 1 H ˛, 77 Se ; T 1 77 Se , T 2 77 Se , T 1 77 Se . The linewidth of the 77 Se resonance of selenocystine is dominated by chemical shift anisotropy relaxation, as shown by its dependence on the square of the magnetic field. The reported parameters will serve as reference data for the biomolecular NMR spectroscopy of 77 Se-labeled proteins where the cysteine has been replaced by selenocysteines.