Aspergillus terreus was used for riboflavin (vitamin B2) production in a medium containing beet molasses as the sole carbon source. Growth and the vitamin production of the fungus were markedly affected by the composition of the culture medium. A maximum riboflavin yield was achieved at the late exponential growth phase (16 day-old cultures) in the presence of (g/l): centrifuged beet-molasses, 90; L-asparagine, 1; MgSO4.7H2O, 0.5; K2HPO4/kH2PO4 (1:1), 5; and the medium initially adjusted to pH 8.