Recently, we reported the successful isolation and pharmacological activities (antihistaminic activity, the influence on blood pressure, etc.) of a new alkaloid, nigrifactin, produced by Streptomyces strain No. FFD-101. Nigrifactin is highly unstable and polymerized promptly on isolation even under inert gas; however, it can be handled in dilute acidic solutions and in the form of its salts such as picrate and flavianate. This communication reports the structure of nigrifactin. Nigrifactin [picrate: m.p. 175.5-176°C (dec.), Anal. Found: C, 53.24; H, 5.05; N, 14.06; O, 28.20. Calcd. for C₁₂H₁₇N·C₆H₃O₇N₃: C, 53.46; H, 4.88; N, 13.86; O, 27.70%; Rf: 0.43 (n-BuOH:AcOH:H₂O=4:1:1); [α]₀° (C=0.5, methanol); pkb=8.8 (50% ethanol); λmax (ε) 354 nm (36700, conjugated double bond) in neutral/acidic methanol; positive Dragendorff (orange), Mandelin (brown), platinic chloride (greenish blue) reactions] shows IR bands at 1610 cm⁻¹ (C=C) and 1000 cm⁻¹; free base has 1645 cm⁻¹ (C=N) and 1610 cm⁻¹ (C=C). UV shows hypsochromic shift on basification (300 nm above pH 9.2, 354 nm in neutral/acidic solutions). Nigrifactin is reduced by PtO₂ to crystalline octahydro compound (II, C₁₂H₂₅N·HCl, secondary amine) with no C=C bands/UV absorption. Dehydrogenation of (II) gives pyridine derivative (III), which matches synthetic 2-heptyl-pyridine (m.p., mixed m.p., IR, mass, UV spectra, pka). These results indicate nigrifactin's structure is 2-heptatrienyl-Δ¹-piperideine (I).