A new indole alkaloid, pendolmycin 111, was isolated from Normdiopsis strain SA 17 15 as an inhibitor of epidermal-growth-factor-induced phosphatidylinositol turnover in A43 1 cells. The structure of pendolmycin is closely related to that of teleocidin B I21 and of lyngbyatoxin A [3]. Pendolmycin may be a biosynthetic intermediate of these alkaloids. In the course of screening for inhibitors of epidermal-growth-factor (EGFbinduced phosphatidylinositol turnover, we have isolated a new indole alkaloid from a strain of Norardiopsis, which we named pendolmycin 117. We report here the isolation, purification, and structure determination of this compound and show that it is structurally closely related to the indole alkaloids, teleocidin B 121 and lyngbyatoxin A 137. Teleocidin B was isolated in 1960 from a Streptomyces species (l), and lyngbyatoxin A was isolated in 1979 from the lipid extract of an Hawaiian shallow-water variety of Lyngbya majuscula Gomont (2). Both teleocidin B and lyngbyatoxin A exhibit irritant toxicity, which is also seen with pendolmycin.