Unconventional natural sources for future drug discovery

'There are more things between heaven and earth... 'Despite the progress of science during the past four centuries, Shakespeare's words did not lose their actuality. Knowledge about the etiology of diseases is still limited, and for many life-threatening illnesses no effective treatments exist. Nature always has been a valuable source of drugs and, despite the unprecedented opportunities afforded by medicinal chemistry, continues to deliver lead compounds. Traditionally, research on natural sources was focused on terrestrial plants and microorganisms. More recently, however, organisms of marine origin are also being investigated. Here, the possibilities of unconventional and hardly explored sources are discussed.