Pheochromocytoma is a tumor that produces a variety of biologically active substances in addition to catecholamines. We report here a patient with a pheochromocytoma, who presented with acute inflammatory symptoms and marked abnormalities in liver function and hematological tests. A 31-year-old man, who had experienced intermittent fever, chills and weight loss during the previous several months, was referred to our hospital for further evaluation. Laboratory examination revealed anemia, leukocytosis with elevated inflammatory markers, and abnormalities in coagulation and liver function tests. Histological examination revealed a marked plasmacytosis in the bone marrow and lymphocyte infiltration into the portal area of the liver. Along with increases in serum catecholamine and urine catecholamine metabolites, his serum interleukin (IL)-6 level was increased to 300 pg/ml, compared with a normal range of 3-12 pg/ml. Left adrenalectomy was performed. The adrenal tumor was densely immunostained with antibody to IL-6. After resection of his adrenal tumor, his serum IL-6 level returned to normal (11 pg/ml) and all symptoms subsided with normalization of laboratory findings.