THE GREAT HONOR that you have awarded me today was unanticipated, and the more treasured because the Association also honors Professor Rous and Professor Whipple, scientists for whom I have the greatest admiration. It is also a happy occasion because it allows me the privilege of acknowledging the men who trained me: HE Rawlinson and RF Shaner at the University of Alberta, and FJ Dixon at the University of Pittsburgh. It is a pleasure to ac-knowledge the support of AJ French during the struggle to become established; and RH Fennell Jr., at the University of Colorado has been a true friend anda constant source of strength and inspira-tion. If I had a brother, I'd like himto be just like Hank Fennell. Finally, I would like to say" Thank you" to the Fellows, Residents, and Students who have contributed so much to this work and bright-ened each day.

In this lecture I propose todiscuss a concept of cancer that has been formulated upon our experi-ments on differentiation and cancer, outline the current experiments from our laboratory in regulation of cancer by the embryo, and indicate the potential importance of this approach for therapy. Despite enormous successes in the treatment of certain tumors, after 30 years of intensive study, the conclusion is unavoidable that alternatives to cytotoxic therapy are desperately needed forthe treatment of carcinoma with metastases. I would propose direction of differentiation of malignant to benign cells as the most promising alternative. This idea is based upon our demonstration in 1959 that embry-onal carcinoma cells of testicular teratocarcinomas could spontaneouslydifferentiate,'and in 1961 that these differentiations could be modulated in vitro. 2 To refresh your memory, a teratocarcinoma is an extremely malignant tumor containing a heterogene-ous collection of differentiated tissues representing each of the primary germ layers, plus embryonal car-