A series of biodegradable, proecological depressants for selective flotation of galena and synthetic chalcocite was tested. These depressants, originating from dextrinization of potato starch with biogenic a-amino acids such as alanine, arginine, asparagic acid, cysteine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, proline, serine, threonine, tryptophane, tyrosine, phenylalanina and valine, appeared to be effective depressants. Among them dextrins from starch modified with asparagic acid, glutamic acid and threonine were superior as they provided good recovery of galena and significant depression of synthetic chalcocite at a concentration of 2-4 kg/Mg of minerals when sulfides were subjected to microfiotation separately. Subsequently, threonine dextrin was tested as a copper mineral depressant for Polish industrial copper concentrates containing 18.28% Cu and 3.63 % Pb. The test was carried out in a laboratory flotation machine and it was found that threonine dextrin was highly selective but the results were opposite to the microflotation tests since it depressed lead mineral more efficiently than the copper minerals