Piedra (stone in Spanish) is the name given to a trichomycosis characterized by the formation of nodules resembling small stones. There are two varieties of the disease, depending on the colour of the nodules: white piedra and black piedra. Black piedra sharply differs from white piedra on three main scores: a) the causative agent is a black filamentous and sexed dematicious fungus, Piedraia hortai; b) the disease exclusively affects the scalp, and c) the geographical distribution of human black piedra is limited to tropical and subtropical areas (South America, South-East Asia). White piedra has a different aetiology, being caused by an asexual fungus, Trichosporon beigeli. The genus Trichosporon (Behrend, 1890) and the species T. beigeli (Vuillemin, 1902) were created from a case of piedra of the moustache. White piedra may involve hairy regions other than the scalp, such as the beard and moustache, less frequently the armpits, eyebrows, eyelashes and pubic hair. The disease has been observed in all continents, except Africa, and under all climates, although it is exceptionally found in cold areas (two indigenous cases in Finland). The observatio princeps of white piedra (on a false chignon) was published in 1865 by Beigel, in London. In France, only three cases, all concerning the moustache, were reported at the very beginning of this century No other case has been published in that country in the east 80 years. T. beigeli is a common saprophyte in nature. It has been found in soil, water, fruit, rotten vegetables, sawdust, as well as in man (skin, skin appendages, mucosae) and in animals (mammals, insects, mussels).(ABSTRACT TRUNCATED AT 250 WORDS)