Biosurfactants containing rhamnose and beta-hydroxydecanoic acid and called rhamnolipids are reviewed with respect to microbial producers, their physiological role, biosynthesis and genetics, and especially their microbial overproduction, physicochemical properties and potential applications. With Pseudomonas species, more than 100 g l(-1) rhamnolipids were produced from 160 g l(-1) soybean oil at a volumetric productivity of 0.3 g l(-1) h(-1). The individual rhamnolipids are able to lower the surface tension of water from 72 mN m(-1) to 25-30 mN m(-1) at concentrations of 10-200 mg l(-1). After initial testing, rhamnolipids seem to have potential applications in combating marine oil pollution. removing oil from sand and in combating zoosporic phytopathogens. Rhamnolipids are also a source of L-rhamnose, which is already used for the industrial production of high-quality flavor components.