The lignoid compound asarinin and the insecticidal and sialogogic compound neoherculin were isolated earlier from the bark of Zanthoxylum clava-herculis L. (Rutaceae) (1-3). In our study of bioactive plants, we found the extract of the bark to be highly toxic to fish, and fractionation was undertaken based on this activity. After a preliminary solvent partition, the extract was chromatographed on silica gel and five crystalline components (A-E) were isolated. Of these, the last two (D and E) were found to be responsible for the toxicity of the extract. Fractions A and B were isomeric with the formula C₂₀H₂₂O₆ (M⁺ 354) and were shown to be identical with (-) asarinin (1) and (-)-sesamin (2), respectively. Both of these belong to the 3,7-dioxabicyclo [3,3,0] octane type lignans, with 1 being the axial/equatorial isomer and 2, the diequatorial isomer. (-)-Sesamin has been found in a variety of plants, including some species of Zanthoxylum, but has not been isolated from Z. clava-herculis previously (4,5). Fraction C, C₂₅H₂₈O₆ (M⁺ 424) showed color reactions and uv spectral characteristics very similar to those of 1 and 2, indicating it belonged to the same general class of lignoids. Through spectral data elucidation (including ¹H-nmr, mass spectrum, and stereochemical analysis), Fraction C was assigned the structure of γ,γ-dimethylallyl ether of (-) pluviatilol (5), which has an axial/equatorial stereochemistry. Fraction D, C₁₆H₁₅NO, the major component, was shown to be neoherculin and the major ichthyotoxic principle of the extract with an IC₅₀ of 2 × 10⁻⁷ M when tested according to the procedure of Stephan (6). Fraction E, C₁₉H₁₇NO₃ showed spectral properties corresponding to the aporphine alkaloids, and its identity with N-acetylanonaine was established. This compound has been isolated from various plant sources (e.g., Magnolia obovata (7) and Liriodendron tulipifera (8)) but not from Z. clava-herculis. N-acetylanonaine was also toxic to fish with an IC₅₀ of 3×10⁻⁴ M.