Polyclonal antibodies collected from the blood of animals and humans experimentally immunised or spontaneously immunised respectively can be injected into patients to protect them against pathogens, toxins, tumours etc. This approach is severely limited by the availability of human polyclonal antibodies of interest. Moreover, polyclonal antibodies from animals are recognised as antigens by patients and are thus rapidly rejected and inactivated. To circumvent this problem, animals (essentially rabbits, chicken, pigs and cows) are being genetically engineered. Their immunoglobulin genes are being inactivated and the corresponding human immunoglobulin genes are being transferred to them. These animals will be immunized and it is expected that large amounts of pure human polyclonal antibodies will be extracted from their blood to be administered to patients. The possible acceptability problem of this approach is under a case study of the European Union Pegasus project.