A team of researchers at the Roslin Institute is trying to produce pigs with the lethal lung condition cystic fibrosis and an eye disease that leads to blindness.
If successful, the animals will then be passed to drug companies who will use them to test new forms of gene therapy being developed for humans.
The research has sparked outrage from animal rights organisations, who described it as "cruel", "fraudulent", "intrusive, harmful, and painful", while the process of harming animals intentionally for human benefit raises major ethical issues.
Dr Bruce Whitelaw, head of developmental biology at the Roslin Institute, admitted he had struggled with the idea.
"We are saying we will make these animals sick purely for our benefit," he said.