<jats:title>Abstract</jats:title><jats:p>A variety of toxic secondary metabolites including fumonisins, can be produced by the fungus <jats:italic>Fusarium moniliforme</jats:italic> and closely related species in section Liseola in large amounts (g/kg in laboratory cultures). Underivatized fumonisins were detected by HPLC using either an evaporative light scattering detector or electrospray MS. Electrospray MS used together with NMR and GC/MS was used to identify a new fumonisin, fumonisin C<jats:sub>4</jats:sub>, which corresponds in structure to fumonisin B<jats:sub>4</jats:sub> with the C‐1 terminal methyl group missing. Several novel strains of <jats:italic>F. moniliforme</jats:italic> mating population A were identified that produced little or no fumonisin B<jats:sub>1</jats:sub>, but large amounts of either fumonisin B<jats:sub>2</jats:sub>, or B<jats:sub>3</jats:sub> together with fumonisin B<jats:sub>4</jats:sub> and C<jats:sub>4</jats:sub>. These strains which do not produce fumonisin B<jats:sub>1</jats:sub> should prove useful in purification of fumonisin B<jats:sub>2</jats:sub>, B<jats:sub>3</jats:sub>, C<jats:sub>4</jats:sub>, and B<jats:sub>4</jats:sub> for toxicology studies. © 1995 Wiley‐Liss, Inc.