Sulfhydryl-compounds play an important role in the maintenance of metabolic processes of the living cell and are implicated in a variety of enzymatic reactions. The decrease in radiation lethality engendered by these agents is well-known. Thioglycolic acid (TG), glutathione and British Anti-Lewisite (BAL) protect against lethal dosages of nitrogen mustard in rats and mice (Brandt and Griffin, '51); cysteine, although greatly reducing the mortality, did not affect the typical leukopenia and allied reactions produced by the mustard. Pretreatment with varying concentrations of cysteine, glutathione and TG produced up to 100% protection against the diabetic syndrome developing on alloxan administration (Lazarow, '47). In this connection, the disulfied linkages in insulin are reduced by thiols, incubation with cysteine (Wintersteiner, '33), TG (Stern and White, '42) and BAL (Barron, Miller and Meyer, '47), among others, destroying the activity of the hormone. The anti-tubercular activity of a series of mercapto-derivatives in mice has been determined and only those capable of yielding ethyl mercaptan on metabolism were effective; TG proved negative (Davies et al., '56). The metabolic studies carried out by Peters on BAL metabolism are classical and the compound has been widely explored from the standpoint of enzyme inhibition (