Spiro-prorocentrimine, C42H69NO13S, is a polar lipid-soluble toxin isolated from a laboratory-cultured benthic Prorocentrum species of Taiwan, crystallized in methanol. X-ray diffraction analysis of the compound revealed a spiro-linked cyclic imine with the ortho, para-disubstituted 3%-cyclohexene in addition to its macrolide skeleton. 13C and 1 H NMR signals were then assigned accordingly. This is the first compound of this group of marine toxins with a clear stereochemistry. © 2001 Elsevier Science Ltd. All rights reserved.