Three strains of the fungus Rhizopus oryzae were screened for their ability to produce fumaric acid on untreated or treated corn distillers` dried grains with solubles. The treatment of the grains included autoclaving alone or with low levels of sulfuric acid. After fungal growth, the grains were processed and fumaric acid production was assayed enzymatically while biomass production was determined gravimetrically. It was found that fumaric acid production by the three strains of R. oryzae after 240 h was higher on the autoclaved grains or acid-hydrolyzed grains compared to the untreated grains. Biomass production by R. oryzae ATCC 20344 after 240 h on the untreated and treated grains was higher than observed for R. oryzae ATCC 10260 and ATCC 52918. Fumaric acid productivity was higher for all three strains grown on the acid-hydrolyzed grains relative to their productivity on the untreated or autoclaved grains.