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Few people would dispute that blood transfusion and renal dialysis have made a huge contribution to clinical medicine in the past few decades. But handling blood still carries many dangers: the chief practical danger is that of transmitting virus infections. It was the recognition of post-transfusion hepatitis that gave the main impetus to the search for viruses that damaged the liver.

One such virus was already known: the so-called hepatitis B virus which is the commonest cause of sporadic jaundice. In 1963 Blumberg discovered the agent that caused most cases of post-transfusion hepatitis, now known as hepatitis B, and for over 20 years, only two agents were clearly identified as hepatitis viruses. But even after careful testing of blood to be used for transfusion and after changes to the design of kidney dialysis machines, there was a residue of "non-A, non-B hepatitis". For a long time it was clear from the epidemiology that this was due to an infectious agent, but the virus was only identified by a very ingenious technique in 1989: this is now known as hepatitis C virus. Recently it has become clear that this virus is very difficult to eradicate in about half of those who become infected; and after many years the infection can lead to cirrhosis and in some cases to liver cancer. Not only blood must now be tested for this virus, but many products such as antibodies that are prepared from blood must be shown to be free of this insidious agent.

As the alphabet of hepatitis viruses grows, it has become clear that the viruses have very little in common, other than the fact that they can damage the liver. Almost every hepatitis virus belongs to a different "family" of viruses, each with a quite distinct pattern of multiplication, survival and spread. Hepatitis A virus, for example, is a distant cousin of the viruses that cause the common cold and those that cause polio: it is mostly spread by contaminated water supplies. The transmission of hepatitis B virus requires much more intimate contact: blood and seminal fluid are the main vehicles used by the virus.

It is a curious fact, still very little understood, that many virus infections are less severe in children than in adults. Mumps and chicken pox are often unpleasant in childhood but in adults they carry a substantially higher risk of serious complications, such as encephalitis or pneumonia. The hepatitis viruses are no exception to this rule. In many parts of the world, hepatitis B virus is very common, and most infected people get the virus from their mothers. In the great majority of children the infection seems to cause no serious disease, although the virus is not eliminated from the body by the immune system in most cases, enabling the children to pass on the virus later in life. But in adults, infection with hepatitis B virus frequently leads to a devastating destruction of the liver, which is frequently fatal. Also in adults, hepatitis B virus is the cause of liver cell cancer which is one of the commonest causes of cancer in the world, and one of the chief causes of early death in adults in areas where the virus is common. A genetically engineered vaccine against hepatitis B virus is very safe and is effective in most people, but there are still enormous practical problems to surmount in interrupting the transmission of the virus in highly endemic areas.

We are slowly beginning to understand the biology of the hepatitis viruses and how they lead to liver damage. As the scientific knowledge grows it is increasingly important that doctors and surgeons should understand its implications for the prevention and treatment of viral hepatitis. It is essential that some people should think about both the science and its practical application, so that opportunities are not lost.

It is also good for scientists to force them out of their corner of the field, to realise that there is more than one hepatitis virus, and that not all problems in hepatitis can be solved in the test tube. This new journal has the potential to benefit both scientists and clinicians in this way: if it can straddle the science and medicine and keep its balance, it will do a great service to both.

Charles Bangham is consultant virologist, John Radcliffe Hospital, Oxford.