The effect of the ratios of thiamine, vitamin B_6 and other vitamins in vitamin B_6 assay medium on the growth of Saccharomyces carlsbergensis 4228 was examined, and it was tried to make clear the mechanism of the antagonism between thiamine and vitamin B_6. The results show that this antagonism was not characteristic to this organisms, but common to a part of Saccharomyces. This antagonism was remarkably affected by balance of pantothenic acid, thiamine and vitamin B_6 in the medium, and it seems to be occurred when the organism required pantothenic acid for the growth but not thiamine and vitamin B_6 cultured in medium containing a small amount of pantothenic acid.