Abstract: The invention concerns new compounds for use in the pharmaceutical industry, its subject-matter being (thio-2-ethyl)-2 carboxy-4 thiazolidinic compounds of the general formula: ##STR1## where R is selected from hydrogen atom, alkyl, phenyl, alkylaryl and acyl radicals, heterocyclic groups such as pyridoxazole or benzimidazole, and alkyl- carboxylic groups, particularly acetic, and esters and amide derivatives thereof, and salts of addition of the compounds. These compounds are of use in the production of medicines with analgesic and mucolytic properties.