In addition to feed safety assessment, including safety for consumers, animals and environment nutritional assessment of feeds produced using recombinant DNA techniques is necessary and should be considered as an essential part of safety assessment. Therefore we need effective systems to assess GMO's in feedstuffs from the nutritional point of view. In 1997 we started a programme to assess GMO's of the so-called first generation including Bt-maize, Pat-maize, Pat-sugar beets and Gt-soyabeans. Digestion and feeding experiments were carried out with broilers (Bt-maize), layers (Bt-maize, Pat-maize), pigs (Bt-maize, Pat-maize, Pat-sugar beet, soyabeans), sheep (Bt-maize silage, Pat-maize silage), growing bulls (Bt-maize silage) and fistulated cows (Bt-maize silage). Up to now, no significant differences in nutritional assessment between feeds from isogenic and transgenic plants of the first generation were found. The so-called substantial equivalence of transgenic hybrids could be demonstrated. Recombinant plant DNA constructs were not detected in animal tissue samples. Proposals for nutritional assessment of GMO including search for unexpected (unintended) effects and aspects of safety assessment are discussed in the paper.