Scientifically, a gene is a part of a chromosome regulating various biochemical processes. Ethically, it is an entity which may be used to influence life for better or for worse. This implies that genetic engineering with animals is only admissible when sound reasons are given. In this regard, there is a resemblance to experimental studies in animals. Two rules of conduct are suggested: (1) Biotechnological research, including genetic engineering, involving (farm) animals for the study and treatment of (genetic) disorders causing unacceptable stress or disease in man and animals, should be stimulated when adequate alternatives are not available. When doing so, adopting measures to minimise negative effects, particularly so in the animals themselves, should be a prerequisite. (2) Biotechnological applications in farm animals for the sole purpose of increasing production or other immediate material objectives should not be pursued, unless it is established that the welfare of the animals is not impaired and their integrity is properly ensured. When negative consequences can be expected for man or society, a solution of these problems should be devised beforehand.