Baruch Blumberg only attended one Lindau Meeting and gave only one lecture. But in this lecture he covered a lot of ground, from the innermost parts of a new virus to large epidemiological surveys. In the introduction (without slides), Blumberg mentioned some of the work that he and his collaborators had done after the 1964 discovery of small protein particles in the blood of an Australian aborigine. It was the discovery of this so-called “Australia antigen” that eventually led to an understanding of how the hepatitis-B virus acts. It also led to the 1974 paper, which pointed out the possibility that there could be a connection between the virus infection and (primary) cancer of the liver. It is interesting to note that when Blumberg mentions the detection method that he had used, radioimmunoassay, the inventor of the method is in the audience. This is the 1977 Nobel Laureate Rosalyn Yalow who, as Blumberg, was a participant of her first Lindau Meeting and had actually lectured on the radioimmunoassay method earlier in the week! Since Blumberg’s 1974 paper, a large amount of epidemiological data had been brought together, which he went on to discuss (with many slides). But first he described the virus. It turned out that the hepatitis-B virus was of a kind that had not been studied before. The main virus particles have both DNA and a varying amount of RNA. They also have two kinds of antigens, core and surface antigens. The latter can separate from the main particle and enter the blood stream, where they can be detected (as shown by the 1964 discovery). Since the virus was of a new kind, producing a vaccine against it could not follow the normal procedure. Instead it was found out that the surface antigen could be used as a vaccine, since injecting this antigen provokes an immune reaction against the main virus particles. Before describing the epidemiological surveys, as a joke, he referred to an advice from a colleague on how to give a lecture: “Say what you are going to say, say it, and say what you just have said!”. From his lecture, it is evident that Blumberg had put a lot of effort not only into making a vaccine, but also in finding out more about the virus, in particular the way it spreads. He had also been interested in looking at the differences between men and women and also in the distribution of virus infections in whole families. It turned out, e.g., that the virus can be transmitted from mother to child over an extended time. Finally, Blumberg carefully discussed the pros and cons of a vaccination campaign at a time before a full understanding of the virus had been found. According to Blumberg, in medicine, which is an emergent subject, one has an obligation to learn more, but also to act. Anders Bárány