This volume is arecord of the proceedings of a NATO Advanced Study institute on "Biochemical and Bio- logical Markers of Neoplastic Transformation" held September 28 - October 8, 1981, at Corfu, Greece. As early as 1860, Rudolf Virchow provided the first genetic concept of cancer by postulating "Omnia ceZZuZa e ceZZuZa ejusdem generis", a modification of the then exisiting cell theory "Omnis ceZZuZa e ceZZuZa". Thus, the idea that all cells originate from the parent cell was extended to the idea that all cancer cells come from the "paren t" cancer cello But how the first cancer cell arose, or in other words, how anormal cell changed to a cancer cell, is, even after 120 years, a mystery. Experimental studies of the past have convinced us that a number of factors contribute to the neoplastic transformation of anormal cell, but our knowledge on the mechanisms involved in this process is still in an embryonic state. In the last few years, however, this field has witnessed a most remarkable advancement cata- lyzed by the development of modern technology in the al lied fields of immunology, the production of mono- clonal antibodies, molecular biology, and sequencing v PREFACE and cloning of ONC genes. Presently, it is becoming more and more evident to the wishful mind of those engaged in this research that we are approaching a turning point. Thus, an assessment of the present situa- tion will be most desirable at this time.