Inhibitors of the bone‐marrow colony formation in sera of patients with leukemia

An increased variation of the bone‐marrow colony stimulating factor (CSF) was found in the sera of patients with acute leukemia as compared to normal sera. In sequential samples from the same patient, there was no apparent correlation between changes in the degree of colony stimulating activity and changes in the clinical and hematologic status. CSF levels as measured in untreated sera seemed to depend upon a variation in serum inhibitor levels. After chloroform treatment, sera from patients with acute lymphoid or myeloid leukemias had higher mean CSF activity than similarly treated normal sera, though the variation was considerable in both groups. The increase was most evident in sera which initially exhibited a normal or low degree of colony‐stimulating activity. In order to evaluate CSF in normal persons and in various diseases, it appears important to remove inhibitory substances efficiently, for instance by chloroform treatment.