In some cases, the infected child will proceed through several stages to the development of PHC. At each stage, only a fraction of the infected individuals will proceed to the next stage, and this will depend on other factors in the host and in the environment. The stages include, retention of the antigen (carrier state), development of chronic hepatitis, development of cirrhosis and finally, development of PHC (Fig. 6). We are currently testing this hypothesis in prospective studies in West Africa (45). If it is true, then prevention of PHC could be achieved by preventing infection with HBV, and the vaccine we have introduced, in association with appropriate public health measures, could reduce the amount of infection. This might also involve the use of gammaglobulin in the newborn children of carrier mothers and such studies are now being conducted by Beasley and his colleagues in Taipei. We are now considering the appropriate strategies that might be used to control hepatitis infection and, hopefully, cancer of the liver.