Quantitative tests for vitamins B (B1) and G (B2) in five samples of yeast showed that the concentration of vitamin B varied considerably (at least 10-fold) in the different samples, while the vitamin G (B2) content of the five samples was relatively uniform. Of the two vitamins the antineuritic vitamin was the limiting factor in three of the samples while vitamin G was the limiting factor in the two samples of brewers' yeast examined.