The dimorphism of Scopulariopsis brevicaulus was induced in malt agar (Oxoid), at 37 degrees C and 5-10% rate of CO2. Six cultures of S. brevicaulus were converted from hyphae to yeast-like cells by the following processes: One was that the hyphae formed intercalar and terminal chlamydoconidia-like cells. These cells increased in size, gained double contour and gave rise to budding cells. The other process was via conidia that assumed yeast characteristics. So, a transformation cycle M----Y was proposed. The yeast-like form presented slow reversion to the mould phase, standing, many times, in transition forms. A high concentration of sugars, peptone, temperature of cultivation of 37 degrees C and 5-10% rate of CO2 seem to be favourable factors for the maintenance of the yeast phase. Ethanol, E.D.T.A., potassium nitrate, temperature of 25 degrees C and aerobiosis are considered favourable factors to conversion of the mould phase.