Glutathione is an intracellular, nonprotein thiol that appears to play an important role in protection of the cell against cytotoxic drugs (1 ) and has been implicated in the control of cell cycling (2 ,3 ) and apoptosis (4 ,5 ). It can exist in an oxidized (disulfide, [GSSG]) and a reduced (sulphydryl, [GSH]) form. In general, GSSG comprises less than 1% of the total intracellular glutathione. In circumstances of oxidative stress, GSH dimerizes to form glutathione disulfide (GSSG), making protons available to neutralize reactive oxygen species (Reaction 1 ). In vivo, reduction of GSSG is catalysed by glutathione reductase, efficiently regenerating high intracellular GSH levels (Reaction 2 )