Medical researchers have come a step closer to making artificial blood. A human blood substitute could be an extremely useful - and valuable - product. Blood for transfusions is used in a great variety of medical procedures, but supplies depend on the goodwill of donors. And human blood supplies are liable to be contaminated by disease - as happened with the AIDS virus before special blood purification procedures were introduced. Now Dr Kiyoshi Nagai and colleagues in Cambridge, England, have succeeded in making a new and stable artificial form of haemoglobin, the protein in red blood cells which transports oxygen around the body and is therefore essential to life. As a result, says Nagai, artificial blood could be in use in hospitals in 5 years' time.