Effective hydrogen production from starch-manufacturing wastes by microorganisms was investigated. Continuous hydrogen production in high yield of 2.7 mol H-2 mol(-1) glucose was attained by a mixed culture of Clostridium butyricum and Enterobacter acrogenes HO-39 in the starch waste medium consisting of sweet potato starch residue as a carbon source and corn steep liquor as a nitrogen source in a repeated batch culture. Rhodobacter sp. M-19 could produce hydrogen from the supernatant Of the Culture broth obtained in the repeated batch culture of C butyricum and E aerogenes HO-39. Hydrogen yield OF 4.5 mol H-2 mol(-1) glucose was obtained by culturing Rhodobacter sp. M-19 in the supernatant supplemented with 20 mug 1(-1) Na(2)MoO(4)(.)2H(2)O and 10 mg 1(-1) EDTA in a repeated batch Culture with pH control at 7.5. Therefore, continuous hydrogen production with total hydrogen yield of 7.2 mol H-2 mol(-1) glucose from the starch remaining in the starch residue was attained by the repeated batch Culture with C butyricum and E. aerogenes HO-39 and by the successive repeated batch culture with Rhodobacter sp. M-19.