Diabetes was the first example of a human disease that could be attributed to a deficiency of a specific protein (insulin) and that could be corrected by an equivalent derived from animals. That startling success was the inspiration for replacement therapies for other diseases. With the advent of gene technology in the 1970s, a generic method for making human proteins on an industrial scale became available. This provoked a gold rush to start the process of making a host of potentially useful proteins on a commercial scale. The discovery came at a critical moment, when infectious agents had seriously compromised the safety of clinically used blood proteins and hormones of human origin. Using gene technology, blood clotting factor VIII and growth hormone were rendered conclusively free of viruses. Gene technology has now revealed many proteins that have potentially important roles to play in controlling pathological symptoms of hundreds of clinical disorders.