Apart from feed safety assessment including safety for consumers, animals and environment, nutritional assessment of feeds produced using recombinant DNA techniques (Genetically Modified Organism, GMO) is necessary. In 1997 we started a program to assess GMO's of the so called first generation (feed plants with changed tolerance or resistance and with minor changes in content of valuable and desirable ingredients) including Bt-corn, Pat-corn, Pat-sugar beets and Bt-soybeans. Apart from main nutrients (crude protein, ether extract, crude fiber, crude ash), amino acids, fatty acids, minerals, fiber components and some mycotoxins were determined in seeds of corn and soybeans, sugar beets rand silages from corn and sugar beet leaves. Digestion and feeding experiments were carried out with broilers (Bt-corn), layers (Bt-corn, Pat-corn), pigs (Bt-corn, Pat-corn, Pat-sugar beets, soybeans), sheep (Bt-corn silage, Pat-corn silage, Pat-sugar beet silage), growing bulls (Ht.-corn silage) and fistulated cows (Bt-corn silage). Digestibility of nutrients, performance of animals and fate of DNA were investigated. Up to now, we did not find significant differences in nutritional assessment and food quality between feeds from isogenic and transgenic plants the first generation, except a lower mycotoxin-content (deoxynivalenol and zearalenon) in Bt-corn. The so-called substantial equivalence could be demonstrated. Fragments of plant DNA could be detected in some nnimal tissues (e.g. muscle from chicken), but fragments of transgenic DNA were not found. It may be assumed that the transfer of DNA fragments in the body is a process, which takes place constantly and consequently, but it is not a specific problem of genetic engineering. However, the subject should be pursued further. From the point of view of animal nutrition, further studies seem to be necessary on the following subjects: - Nutritional assessment of GMO's with substantial changes in composition (GMO's of second generation) - Influence of GMO's upon animal health and product quality.