A patient with lung cancer is described who exhibited severe systemic derangements of metabolism causing cachexia preceding the appearance of a large bulky tumor. The lung cancer growing in the patient acted as a powerful hypoglycemic factor, setting in motion widespread metabolic disorders. Inappropriate secretion of insulin may be involved in the manifestation of hypoglycemia. However, no ectopic secretion of insulin, glucagon, ACTH and aldosterone appeared to be associated with the carcinoma in the patient. Progressive energy loss from the patient occurs by virtue of a combination of severe anorexia and the establishment of a systemic energy-losing cycle dependent on an interplay of glycolysis in the cancer cells and stimulated gluconeogenesis in the host tissues, which is turn results in derangements of protein, lipid and electrolyte metabolism. Attempts to ameliorate the patient''s distress and counterbalance the effect of the tumor by parenteral hyperalimentation were not satisfactory and resulted in only a temporary improvement. This study also demonstrated that marked granulocytosis was the result of production of an excess granulopoietic colony stimulating activity by the cancer cells.