Chlorella vulgaris, a unicellular green algae, has been studied in a variety of practical approaches. In the last years, several reports from our laboratory and others demonstrated the protective effects of this algae against bacterial and virus infections, tumours and peptic ulcers. Recently, the use of C. vulgaris for the removal of toxic metals from natural waters or waste waters has been reported by several authors. This micro-algae has been used for analytical purposes to quantitatively recover ions, such as lead, cadmium, chromium and nickel, from natural water samples. These experiments demonstrated the presence of very high affinity metal ion binding sites in these organisms. This metal-binding property seems to be related to the presence of chloroplast in the cellular wall, an organelle rich in sulphur, potassium, calcium and phosphorus. The ability of sulphydryl-containing compounds to chelate metals is well established in the literature and this could be the main factor involved in the in vitro removal by C. vulgaris of heavy metal con-taminants.