The literature concerning blood histamine has been reviewed, including the evidence that the incorporation of histamine within the myeloid leukocytes may be one of the metabolic functions of myelopoiesis. Data are presented on the histamine content of blood in normal subjects and in subjects with acute leukemia, chronic myelocytic leukemia, erythremia, and with leukocytoses or leukemoid reactions of other etiologies. The changing relationships of total blood histamine to unit myeloid cell histamine in subjects receiving irradiation therapy for chronic myelocytic leukemia are also presented.

The data indicate that total blood histamine in chronic myelocytic leukemia is usually very high in comparison to normal, that the values in erythremia show a definite but less marked tendency in the same direction, while the values in leukocytoses of other etiology are, with few exceptions, normal or low. The blood histamine per million myeloid cells is, on the average, about twice normal in subjects with chronic myelocytic leukemia, within the normal range or a little low in erythremia, and very low on the average in the group of leukocytoses studied. The suggestion is tentatively made that an aberration in this metabolic process (histamine incorporation within myeloid leukocytes) may be an inherent component of chronic myelocytic leukemia, whereas in physiologic leukocytoses and leukemoid reactions this is not the case.

ACKNOWLEDGMENTS The authors wish to express their grateful appreciation to Mr. John Fuschetti for valuable technical assistance in performing the histamine determinations. The cooperation and aid of Dr. Gurth E. Carpenter, Dr. Henry H. Henstell, Dr. Myron Prinzmetal and of many members of the staff of Wadsworth General Hospital, Veterans Administration, Los Angeles were invaluable in obtaining blood specimens from suitable clinical material, and to them the authors wish to express their sincere thanks.