Resin from lignum vitae, the wood of Guajacum officinale L. or G. sanctum L., Zygophyllaceae. Constit. About 70% α- and β-guaiaconic acids, about 11% guaiacic acid, related compds and guaiaretic acid, 15% vanillin, guaiac yellow, guaiac saponin (guaiacin). Use as clinical reagent for occult blood: R. H. Wilkinson, W. A. F. Penfold, Lancet 2, 847 (1969). Acute toxicity: P. M. Jenner et al., Food Cosmet. Toxicol. 2, 327 (1964).