Algae - selected pharmaceutical and toxicological aspects. Algae are ubiquitous organisms that inhabit almost all ecological niches. They belong to Procaryota, Mezocaryota and Eucaryota and come with the sizes from fraction of millimeter to more than a hundred meters. Algae have been widely used by humankind from the ancient times up to day. Initially as a food, and a source of many useful substances at present. The polysaccharides from algae were recognized first as having special rheological properties a long time ago, with the markets worth several billions of dollars a year now. Some species are highly toxic due to the presence of special peptides, alkaloids or other compounds. The substances often display excellent pharmacological properties, when modified or per se being perfect lead structures for pharmacy and experimental medicine. Algae also make a "deep well" of many food supplements as for example unsaturated fatty acids, carotenoids, minerals (e.g. iodine), etc. and there is a plethora of algal cosmetics as well. Some of the above aspects are the plot of this review article.