It is in dealing with malignant disease of the blood-forming organs that teamwork between the radiologist and pathologist assumes its utmost importance, for here one faces so often a changing situation. In this group of malignant processes, it is impossible to catalogue once and for all time a given form of lymphoma or leukemia and be certain that it will retain that form throughout its course. Serial biopsies are frequently informative, and the more cases followed in such fashion, the clearer the point I have just made will become. I do not recommend slowly taking the patient to bits, but a second or third biopsy, or even more, especially at times when the disease is not responding as anticipated, will in the long run do more good than harm. Close observation of the blood picture, as well, by a pathologist who has had clinical contact with the patient is another requirement. Alterations in the character of the disease can often be anticipated by this means. With this preamble, let us turn to tumors gener...