1. Methods for continuous intervenous, arterial venous, and interarterial cross transfusions in man have been developed and a total of seven procedures have been successfully performed.
2. The interarterial method was preferred for an investigation of the pulmonary leukocyte removal mechanism and has been carried on for as long as twenty-six hours exchanging 150 liters of whole blood both to and from each participant.
3. On three occasions within twelve hours after the cross transfusions were terminated, a marked decrease in the leukocyte count occurred in 1 leukemic participant. Marked generalized improvement in the leukemic status occurred after each drop in the leukocyte count.
4. By cross transfusing an adult with myelogenous leukemia and a child with lymphogenous leukemia it was possible to pass myeloid cells through the pulmonary leukocyte removal mechanism into the circulation of the patient with lymphogenous leukemia.
5. An excessive leukocyte removal mechanism was demonstrated during another cross transfusion by a patient with sub-leukemic lymphogenous leukemia.
6. Cross transfusion in man is experimental and offers a technic of value as an investigative method for the study of formed elements and chemical constituents of the blood under these circumstances.
7. Careful cross matching for compatability of blood and Rh type is essential and the hazards and risks of the procedure have been emphasized.