The cultivation of genetically modified plants (GMP) increased from 1.7 to 81 million. ha from 1996 to 2004 (James, 2004). Scientists and farmers, but also consumers, are asking for a nutritional assessment, including safety aspects, of feeds from those plants. Substantial equivalence was created as a framework for the compositional assessment of feeds from GMP of the so-called first generation (without substantial changes of composition or without output traits) and is widely accepted.  However, comprehensive studies are necessary for feeds from GMP of the second generation, with substantial changes in composition and nutritional value or so-called output-traits.The paper summarizes proposals for the nutritional assessment of feeds from GMP of the first generation and discusses experimental designs for assessing feeds from GMP of the second generation.