An agent largely accele rating the growth of propionic acid bacteria (Propionibacterium shermanii l; Propionibacterium freudenreichii 3 and Escherichia coli 113-3, a mutant showing deficiency of Vitamin B₁₂ and methionine) was separated from enzymatic hydrolysate of casein and from autolysate of brewer's -yeast cell biomass.