Luteoreticulin, a new toxic metabolite, m.p. 184.5-185', C H NO (Found : 19 19 5 C, 66.61; H, 5.60; N, 4.12; M+, 341.124; C19H19N05 requires C, 66.85; H, 5.61; N, 4.12; M+, 341.126)', AE:zH 225, 256 (infl.) and 368 afl (& 13,000, 6,000 and 14,400), p ~~~'3 3000, 1599, 1521 (aromatic), 1551, 1348 (-N02), 1688 and 1635 -1 cm , was isolated from acetone extracts of the mycelial cake of Streptomyces luteoreticuli Arai (1) by us and we wish to present its structure elucidation in this communication.