D. desulfuricans and other strains of sulfate-reducing bacteria grew in a liquid medium containing peptone, yeast extract and glucose. Partial and complete hydrolysates of casein were active, but would not entirely replace the yeast extract and peptone. In media without peptone and yeast extract, 4 amino acids (cysteine, serine, ornithine, and isoleucine) had a growth-promoting effect. A large number of biologically active substances were tested and were inactive. Chemical tests suggest that the missing factor or factors is a polypeptides.