Proteins are involved in a majority of the biochemical events that take place in all living organisms. Protein synthesis is directed by genes. All genes contain two major DNA regions. The region containing the genetic message proper (the 'coding region') is preceded by a regulatory region ('the promoter'), which determines when and in which organs a given gene must produce the corresponding protein. The techniques of genetic engineering allow the association of the coding region from one gene with the regulatory region from another gene. The expression of these recombinant genes may be achieved in cultured cells, in transgenic animals or in plants. This leads to the production of the corresponding proteins, including pharmaceutical proteins. Milk from transgenic animals is one potential source of pharmaceutical proteins. To achieve this, the promoters from milk protein genes are bound to DNA fragments containing the coding region of the genes of interest. The desired proteins are then taken from the milk and purified. Two human pharmaceutical proteins are on the market and about 20 projects are in development. One of the proteins produced in milk, antithrombin III, is an anticoagulant and the other, human C1-esterase inhibitor, is an anti-inflammatory. Several human proteins have been produced in the egg white of transgenic chickens and one has been approved by the United States Federal Drug Administration. This process has also been used to modify antibodies in cows. The genes that code for antibodies in the cow were deleted and replaced by human antibody genes. These cows, immunised by various antigens, then secreted purely human antibodies in their blood. Antibodies from such cows were able to attenuate the effects of Ebola virus in human patients.