To scientists, oncology means research on the disease of cancer. The connection between basic research and clinical oncology, however, is not always very clear. Basic research sometimes appears to be an art that is practiced for its own sake and admired for its perfection. The clinician wishes to interpret the issues addressed by basic research, as he is eager to obtain answers to the questions that clinical oncology leaves open. These are, among others, questions as to the etiology and pathogenesis of neoplasma in human beings. In spite of all the technological advances during the past 10 years, the guidelines for new treatments of human leukemias and tumors are still unsatisfactory. The dialogue between researchers and clinicians must never cease, so that these questions can be formulated in such a way that science may be able to answer them. Both parties should cooperate whenever this is useful and possible. Prospectively planned clinical trials on the diagnosis and therapy of neoplasias offer a good opportunity for research involving patients. Tumor and/or blood tests run by reference laboratories on a great number of patients with the same diagnosis can lead to clinically relevant basic research. Using clinical studies in basic research programs permits us to trace missing pieces in the puzzle of cancer and put them into place.