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Vanillin-HCl procedures are widely used for the assay of tannins in plants. In attempts to adapt such procedures for use with sorghum [Sorghum bicolor (L.) Moench.] forage it was found that false positive reactions resulted, that is, red color developed in the presence of HCl with or without vanillin. Leucoanthocyanidins (monomeric proanthocyanidins) may be the constituents responsible for this red color. A "chloroform-HCl" procedure was developed for measuring leucoanthocyanidins in sorghum forage. The procedure avoids interference by chlorophyll or other chloroform-soluble constituents. With vanillin added to the solution, this procedure should also be useful for the assay of condensed proanthocyanidins (tannins).