Granulocyte kinetic studies with DFP32 were done in four patients with chronic myelocytic leukemia, three patients with polycythemia vera, one patient with essential thrombocythemia, and one patient with persistent, unexplained granulocytosis. The increased blood granulocyte concentration found in the patients with polycythemia vera, essential thrombocythemia and unexplained granulocytosis was at least in part the result of increased granulocyte production. Precise calculations of granulocyte pool sizes and turnover rates in the patients with chronic myelocytic leukemia were not possible because of unresolved problems related to the non-uniform population of myeloid cells in the blood of these patients. However, within the limitations of the method, a greater number of myeloid cells were turned over per day through blood than in normal subjects. The findings support the concept that a widespread disorder of marrow proliferation exists in chronic myelocytic leukemia, polycythemia vera, and essential thrombocythemia.