Mycelial growth of Sclerotium rolfsii Sacc. was prolonged, initiation and maturation of sclerotia were delayed, and fewer sclerotia were formed, when ethanol was added to the growth medium at concentrations from 0·5 to 3% (v/v). Similar changes were induced by exposing colonies to ethanol vapour at various stages before the initiation of sclerotia. On liquid glucose-containing medium, total dry weight was little affected by ethanol levels from 0·5 to 3% (v/v). Lower levels of ethanol (0·5–1·5 %, v/v) caused stimulation of total growth, but the relative amount of sclerotial growth decreased with increasing ethanol concentration. The fungus grew sparsely with ethanol as the sole source of carbon. The growth of three other isolates of S. rolfsii and one of Sclerotinia sclerotiorum (Lib.) de Bary was similarly affected by ethanol.