The D-isomer of the naturally-occurring tripeptide glutathione (gamma-L-Glu-L-Cys-Gly, L-GSH) has been synthesised using the Fmoc solid phase peptide synthesis strategy. The D-GSH obtained has been nitrosated to give the D-isomer of the bioactive thionitrite, S-nitroso-L-glutathione. The biological activity of both enantiomers of S-nitrosoglutathione has been studied and compared to the activity of the D- and L-isomers of N-acetyl-S-nitrosopenicillamine (SNAP) and S-nitrosocysteine (CysNO).