Toby K. Eisenstein Symposium Committee Chairperson Temple University School of Medicine Philadelphia, Pennsylvania 19140 This symposium is the thirteenth biennial clinical microbiology program sponsored by the Eastern Pennsylvania Branch of the American Society for Microbiology in cooperation with the Philadelphia area medical schools and the Bureau of Laboratories of the Pennsylvania Department of Health. This year a generous contribution from Merck, Sharp and Dohme has helped to make the program a reality. The subject matter for this symposium represents an attractive spectrum of medical, biological and molecular approaches to the practical solution of a public health prob1em--name1y, prevention of infection with the hepatitis B virus. The symposium may be unique in that it focuses on a product which was first marketed less than three months ago, but included in the program are presen­ tations on two new approaches to hepatitis B vaccine production which may replace the one which is newly unveiled. The rapidity of progress in our present era of biological research is indeed astonishing.