A new base with the composition C29H45NO3 has been isolated from the plant Petilium raddeana and has been called radpetine. Its structure has been established as 3β-hydroxy-23,28-epoxy-23-ethyl-Δ22(N)-22,26-iminocholestan-y-one-by the x-ray structural method (diffractometer, CuKα, 1046 reflections, direct method, MLS in the anisotropic approximation, R = 0.118). Radpetine belongs to a new type of steroid alkaloids with a spiro-methyloxirane grouping at C-23 in the azomethine ring F. © 1991 Plenum Publishing Corporation.