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Summary: The disappearance from the blood was studied of (1) leucocytes of patients with chronic granulocytic leukaemia labelled in vitro with DF32P and irradiated with 1500 rad, and (2) in vitro labelled normal marrow leucocytes. These studies made it possible to estimate the intravascular phase of the lifespan of mature leukaemic neutrophils and to compute the granulocyte turnover rate when immature leucocytes (myelocytes) were present in the blood. The studies support the hypothesis that immaturity of the leucocytes per se may result in their sequestration from the blood stream. The results suggest that granulocyte production is increased in chronic granulocytic leukaemia in relapse, and that the tendency for the leucocytosis to occur may be potentiated by a prolongation of the lifespan of the mature neutrophils. However, this prolongation is only manifest in the presence of leucocytosis.

Leukokinetic studies were performed using granulocytes labeled in vitro with radioactive diisopropylfluorophosphate (DFP32). The half-time of the granulocytes in the circulation, blood granulocyte mass and granulocyte turnover rates were determined. In control subjects the mean half-life was 6.44 hours with a range of 5.1 to 7.7 hours. The mean blood granulocyte mass was 38 x 109 cells with a range of 19.9 to 36.4 x 109 cells and the granulocyte turnover rate was 4.08 x 109 cells per hour with a range of 2.51 to 5.50 x 109 cells per hour. There was a direct relationship between the half-life and the blood granulocyte mass in the control subjects. In 6 subjects with infection the blood granulocyte mass was uniformly increased. The mean half-life and mean granulocyte turnover rate were both increased above the normal range. In 11 subjects with carcinoma several different leukokinetic patterns were found. The blood granulocyte mass was raised in 5 patients, but in only one of these was the granulocyte turnover rate increased above the normal range. In 6 subjects the blood granulocyte mass was within the normal range and deviations from the mean control value were accompanied by proportionate changes in the granulocyte turnover rate in all but 1 patient. No relation was found between the half-life and the blood granulocyte mass in subjects with infection and/or carcinoma. The possibility that this was due to the establishment of a new steady state of blood granulocyte mass at altered levels of granulocyte production, or that steady state conditions did not exist has been considered. However the data are interpreted no evidence for suppressed granulopoiesis was found in subjects with advanced malignant disease.