Abstract: The present invention covers D or L or DL-cysteine derivatives of the general formula (I) ##STR1## wherein R represents H or a fatty saturated or unsaturated acid radical, or a radical of an aromatic acid such as benzoic, cynnamic, salycilic, 2-acetoxybenzoic acid or a heterocyclic acid, as well as their salts, in particular the Ca and Mg salts.The invention refers also to a process for preparing said derivatives and to the pharmaceutical preparations containing them as active principle, having a bronchial liquefying and expectorating activity.