An exact colorimetric method of analysis for determining nicotinic acid in aq. soln. is elaborated. The method depends on the addition of CNBr at 70-80[degree]F and the production of a color with metol (p-methylaminophenol sulphate) at room temp. The color obtained is a clear yellow one, very stable and of an intensity directly proportional to the amt. of nicotinic acid. For the detn. of nicotinic acid in biological material this is dissolved in NaOH on the boiling water-bath and after neutralisation with HC1, the nicotinic acid is extracted with acetone. The acetone extract is transferred to water before the analysis is carried out. The method is employed to analyse samples of yeast. From 16 to 61 mg. of nicotine acid % dry wt. are found in the various types of yeast.