This document describes a procedure for the determination of phomopsins in lupin seeds and lupinderived products based on liquid chromatography with tandem mass spectrometry (LC-MS/MS). Several phomopsins exist@ i.e. phomopsin A@ B@ C and D@ but the method only deals with the quantitative measurement of phomopsin A due to lack of commercially available analytical reference standards for the other phomopsins. The method has been validated for phomopsin A in naturally contaminated lupin seeds@ lupin flour and crisp bread at levels ranging from approximately 5 ??/kg to 60 ??/kg.