Methods are described for the determination of leuco base in FD&C Blue No. 1 by reverse phase liquid chromatography and for the preparation and standardization of leuco base stock solution. The stock solution is prepared by reductive titration of the color with TiCl3. Solutions of the color and of leuco base are chromatographed by isocratic elution, which is followed by a wash and equilibration that can be omitted for screening. Peak area and height calibrations were linear. At the specification level, the 99% prediction limits were 5.00 +/- 0.14% (area) and 5.00 +/- 0.37% (height). Limits of determination were 0.29% (area) and 0.73% (height) at the 99.5% confidence level. Recoveries were 97-101% for leuco base added to FD&C Blue No. 1 at levels of 1-6%.