A review of the history of the knowledge of the development of DNA was presented on the symposium 'Biotechnology'. Entirely in agreement with expectations, genetic manipulation became suitable for use, also in farm animals, approximately thirty years after the discovery of the double helix. The technology available for transfection is limited and is only successful in a small number of cases: less than one per cent. In addition, gene constructions give rise to a large number of problems as they are not tissue-specific and fail to function at the correct time in the course of development. The knowledge of interesting genes (at DNA level) in farm animals is of vital importance. Detecting these genes will undoubtedly still require considerable effort. In view of the technical state of things, medical and physiological studies using transfection will obviously have to provide a new insight prior to use. This is in agreement with the memorandum on 'Ethics and Biotechnology in Animals'. A 'no, unless' procedure is recommended in this note, room being left for 'good' objectives of research following ethical consideration.