Technical Abstract: A thorough review of the biochemical aspects is contained in the - Environmental Health Criteria 219: Fumonisin B1 (FB1) - published by the International Programme on Chemical Safety (IPCS), Geneva, 2000 (EHC 219). Following summarizes that review with an update of relevant new publications. With a few exceptions, only references that were not included in the IPCS monograph, recent or critical reviews, or studies documenting stated dosages are cited here. Many in vivo animal studies on fumonisins have utilized culture materials and naturally contaminated maize in which can be found FB1, but also FB2 and FB3. Studies in different biological test systems have been conducted on the different chemical derivatives of the fumonisins to gain insight into the structural requirements of fumonisin-induced in vivo toxicity and biochemical mechanisms. Briefly, where investigated fumonisins of the B series are more toxic in vivo than their hydrolysed (HFB1=AP1 and HFB2) or N-acetylated counterparts (FA1 and FA2). A specific role for the free amino group is important, as the N-acetyl derivatives are less toxic in primary hepatocytes, although HFB1 is more toxic. The reduced toxicity of HFB1 in rat liver is not due to reduced absorption. Frequent reference will be made to Fusarium verticillioides (Sacc.) Nirenberg, the fungus previously referred to as Fusarium moniliforme Sheldon. Throughout the document, where dose levels have been calculated from dietary fumonisin concentrations, the resulting calculated doses are indicated as "equivalent to" using the conversion factors provided in the JECFA guidelines for preparation of working papers.