questions and future experiments. Further details were provided by posters. The proceedings of the meeting are published in this volume. We feel that many open questions and facts described here will provide stimulating ideas and a basis for further investigation of this fundamental process. The success of the workshop would not have been possible without the help of many people. We are very grateful to the German Cancer Research Center for its interest and assistance, and for the support of the Verein zur Forderung der Krebsforschung in Deutschland represented by Prof. Dr. h.c. K.H. Bauer, the ECBO (European Cell Biology Organization) and the Deutsche Gesellschaft fur Zellbiologie. Our sincere thanks are also extended to our students and technicians for their enthusiastic help, and to Mrs. Joa for typing the manuscripts.