A subcutaneous tumor of the right temporal region of head was removed from an 8‐year‐old boy. This tumor was studied by light and electron microscopy. He was found to have had a retroperitoneal inflammatory fibrous histiocytoma which had been excised seven years ago. The subcutaneous tumor histologically consisted of spindle cells in fascicles, which did not arrange in a storiform or herring‐bone pattern. Electron microscopically, this tumor was chiefly composed of myofibroblasts. Electron microscopy is essential to determine the cell types of a tumor and we have classified this tumor as a tumor of myofibroblasts. The relationship between the retroperitoneal tumor and the head tumor was discussed.

Seven transplantable leukemias and lymphomas which occurred in NZB mice were characterized immunologically and cytologically as B‐cell type of L66‐, 2709‐, 2769‐find S77‐lines, and T‐cell type of TH17‐, TH90‐and 829‐lines. These were also studied with enzyme histochemistry in tissue sections. All B‐cell tumors revealed strong activities of ATPase and 5′‐nucleotidase and one expressed AlPase activity on the cell surface. Two thymic lymphomas (TH17‐and TH90‐lines) and one T‐cell leukemia (S29‐line) showed negative reactions of ATPase and 5′‐nucleotidase but positive activities of AcPase and non‐specific esterase localized in their cytoplasms. AlPase activity was expressed in TH90‐lymphoma but not in TH17‐and S29‐lymphomas. AlPase recognized in L66‐and TH90‐lymphomas showed similar reaction to those of Nagao's isoenzyme. The splenic follicles of normal NZB mice reacted to ATPase and 5′‐nucleotidase in B‐cell area (primary follicles) and to AcPase and non‐specific esterase in T‐cell area (PALS) with the localized reaction. Data suggest that four enzymes of ATPase, 5′‐nucleotidase, AcPase and non‐specific esterase are useful for the differentiation of B‐and T‐cells and their malignant counterparts.

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