guiding research and experimental studies on animals, also the first human trials of new therapeutic agents which have been fully tested on animals. The Co-operating Groups carry out com­ plementary testing involving large numbers of patients. Thus, OER TC is not a "learned society" but an agency for co- ordinating work. OER TC's annual plenary meeting for 1968 was held in Paris on 22nd and 23rd March. It was given over to an intensive study of the scientific basis of chemotherapy in the treatment of cancer in man. These two working sessions brought together members of all groups, both directing and co- operating. The first day was in effect a teaching seminar, open to all practitioners wishing to use chemotherapy in cancer, and explaining the scientific basis of such treatment. This seminar constitutes the present monograph.