Early detection of cancer has been recognized as an important area of preventive medicine for quite some time. In a few sites, such as the cervix, the breast, and the skin, it has been shown beyond doubt that early detection and secondary prevention of cancer are realistic goals. However, the general success of this approach is limited and re quires substantial additional effort in research and public health education. The present volume is based on an International Symposium on Cancer Diagnosis - Early Detection, which was organized by the Committee Coordinating Cancer Research in GroBforschungsein richtungen of the Federal Republic of Germany. The meeting was held at the German Cancer Research Center in Heidelberg, June 3-15, 1991. I am grateful to all members of the Scientific Committee who gave valuable advice in preparing the program of the conference: Gunther Bastert (Heidelberg), John Collins (Braunschweig), Heinz Hofler (MunichINeuherberg), Ernst Jung (Mannheim), Gerhard van Kaick (Heidelberg), Stefan Meuer (Heidelberg), Michael Wannenmacher (Heidelberg), and Wolfgang Wilmanns (Munich/ Neuherberg). I am obliged to Volker Diehl (Cologne), Gunther Bastert (Heidelberg), Hans K. Miiller-Hermelink (Wiirzburg), Manfred Schwab (Heidelberg), and Georg Dhom (Homburg/Saar) for serving as chairmen of the sessions. I am also grateful to Horst Metzler and the administration of the German Cancer Research Center for all their efforts to guarantee a smooth running of the Conference."