A new tetrodotoxin analogue, 1-hydroxy-5,11-dideoxytetrodotoxin, was isolated from the newt Taricha granulosa, and its structure was determined. It is the first example of an N-hydroxy and 5-deoxy derivative of tetrodotoxin found in nature, and its discovery may be highly significant with respect to the biosynthesis of tetrodotoxin and its toxigenesis in various tetrodotoxin-containing organisms.