Simmondsin, a monoglucoside extracted from seeds of the jojoba plant (Simmondsia californica), has been shown to be 2-(cyanomethylene)-3-hydroxy-4,5-dimethoxycyclohexyl β-D-glucoside (1). Preliminary investigations in this laboratory indicate that incorporation of jojoba meal into the diet of weanling rats causes extreme weight loss, reflecting failure of the animals to consume food. Extraction of ground jojoba seed in succession with heptane, benzene, ethyl acetate, and methanol concentrated the active substance in the ethyl acetate fraction; chromatography on silica gel yielded a crystalline component exhibiting feeding inhibition activity, termed simmondsin. Analysis of the n.m.r. spectra of simmondsin and its penta-acetate permitted assignment of the stereochemistry and the point of attachment of the glucose. Hydrolysis with β-glucosidase established the β-linkage and confirmed the glucose unit. The mass spectral parent ion of the penta-acetate (mass 585.201) was consistent with the formula C₂₇H₃₁NO₁₄, corresponding to C₁₇H₂₅NO₉ for simmondsin. I.r. (2218, 1640 cm⁻¹) and U.V. (217 nm) spectra supported an α,β-unsaturated nitrile. Acid treatment gave 2-hydroxy-5-methoxyphenylacetic acid and its lactone; basic degradation yielded 2-hydroxy-3-methoxyphenylacetonitrile, further verifying the structure.