Abstract: The present invention provides 6,8-Dimercaptooctanoic acid derivatives substituted at the 6-S and/or 8-S position with the (3-methylthiopropanoyl) radical, wherein they correspond to the following formula (I): ##STR1## in which: R represents OR.sub.3 or ##STR2## R.sub.3 representing a hydrogen atom, a linear or branched alkyl radical, or a radical of the formula ##STR3## n being an integer from 1 to 10 and r' and r", which are identical or different, representing a hydrogen atom, a linear or branched alkyl radical or, taken together, form with the nitrogen atom, a nitrogen-containing heterocycle optionally substituted with an optionally substituted oxygen or nitrogen atom,R.sub.5 and R.sub.4, identical or different, represent a hydrogen atom or a linear or branched alkyl radical,R.sub.1 and R.sub.2, which are identical or different, represent a hydrogen atom, a radical --COCH.sub.3 or a radical of formula:--CO(CH.sub.2).sub.2 SCH.sub.3 (II)with the proviso that at least one of the radicals R.sub.1 or R.sub.