A cysteine prodrug having the structure: wherein: R 1 and R 2 are independently selected from OH, =O, or a branched or straight chain C 1 to C 5 alkoxyl group, with the caveat that when =O is selected the nitrogen atom adjacent the carbonyl group thusly formed bears a H and a single bond joins the adjacent nitrogen to said carbonyl group; R 3 is H, a branched or straight chain C, to C 5 alkyl, a nitrobenzenesulfonyl, a trityl, an aryl thio, an aryl, an alkylthio, an acyl, a benzoyl, a thio acyl, a thio benzoyl, or a benzyl group; and R 4 is selected from the side chain groups of the natural L-amino acids gly, ser, arg, asp, glu, gln, ile, lys, met, thr, trp, D-isomers thereof, or a cys side chain group protected by a group selected from nitrobenzenesulfonyl, a trityl, an aryl thio, an aryl, an alkylthio, an acyl, a benzoyl, a thio acyl or a thio benzoyl group, with the caveat that when R 4 is the side chain group of the natural L-amino acid gly, R 1 and R 2 are not both selected to be =O; or a cystine dimer of said prodrug having the structure: wherein: R 1, R 2, R 5 and R 6 are independently selected from OH, =O, or a branched or straight chain C 1 to C 5 alkoxyl group, with the caveat that when =O is selected the nitrogen atom adjacent the carbonyl group thusly formed bears a H and a single bond joins the adjacent nitrogen to said carbonyl group; and R 4 and R 7 are independently selected from the side chain groups of the natural L-amino acids cys, gly, phe, pro, val, ser, arg, asp, asn, glu, gln, ala, his, ile, lys, met, thr, trp, D-isomers thereof or a cys side chain group protected by a group selected from a branched or straight chain C 1 to C 5 alkyl, a nitrobenzenesulfonyl, a trityl, an aryl thio, an aryl, an alkylthio, an acyl, a benzoyl, a thio acyl, a thio benzoyl or a benzyl group, with the caveat that when R 4 and R 7 are both the side chain group the natural L-amino acid gly, R 1, R 2, R 3 and R 6 shall not all be selected to be =O. wherein: R 1 and R 2 are independently selected from OH, =O, or a branched or straight chain C 1 to C 5 alkoxyl group, with the caveat that when =O is selected the nitrogen atom adjacent the carbonyl group thusly formed bears a H and a single bond joins the adjacent nitrogen to said carbonyl group; R 3 is H, a branched or straight chain C, to C 5 alkyl, a nitrobenzenesulfonyl, a trityl, an aryl thio, an aryl, an alkylthio, an acyl, a benzoyl, a thio acyl, a thio benzoyl, or a benzyl group; and R 4 is selected from the side chain groups of the natural L-amino acids gly, ser, arg, asp, glu, gln, ile, lys, met, thr, trp, D-isomers thereof, or a cys side chain group protected by a group selected from nitrobenzenesulfonyl, a trityl, an aryl thio, an aryl, an alkylthio, an acyl, a benzoyl, a thio acyl or a thio benzoyl group, with the caveat that when R 4 is the side chain group of the natural L-amino acid gly, R 1 and R 2 are not both selected to be =O; or a cystine dimer of said prodrug having the structure: wherein: R 1, R 2, R 5 and R 6 are independently selected from OH, =O, or a branched or straight chain C 1 to C 5 alkoxyl group, with the caveat that when =O is selected the nitrogen atom adjacent the carbonyl group thusly formed bears a H and a single bond joins the adjacent nitrogen to said carbonyl group; and R 4 and R 7 are independently selected from the side chain groups of the natural L-amino acids cys, gly, phe, pro, val, ser, arg, asp, asn, glu, gln, ala, his, ile, lys, met, thr, trp, D-isomers thereof or a cys side chain group protected by a group selected from a branched or straight chain C 1 to C 5 alkyl, a nitrobenzenesulfonyl, a trityl, an aryl thio, an aryl, an alkylthio, an acyl, a benzoyl, a thio acyl, a thio benzoyl or a benzyl group, with the caveat that when R 4 and R 7 are both the side chain group the natural L-amino acid gly, R 1, R 2, R 3 and R 6 shall not all be selected to be =O. wherein: R 1, R 2, R 5 and R 6 are independently selected from OH, =O, or a branched or straight chain C 1 to C 5 alkoxyl group, with the caveat that when =O is selected the nitrogen atom adjacent the carbonyl group thusly formed bears a H and a single bond joins the adjacent nitrogen to said carbonyl group; and R 4 and R 7 are independently selected from the side chain groups of the natural L-amino acids cys, gly, phe, pro, val, ser, arg, asp, asn, glu, gln, ala, his, ile, lys, met, thr, trp, D-isomers thereof or a cys side chain group protected by a group selected from a branched or straight chain C 1 to C 5 alkyl, a nitrobenzenesulfonyl, a trityl, an aryl thio, an aryl, an alkylthio, an acyl, a benzoyl, a thio acyl, a thio benzoyl or a benzyl group, with the caveat that when R 4 and R 7 are both the side chain group the natural L-amino acid gly, R 1, R 2, R 3 and R 6 shall not all be selected to be =O.