Followings are the results derived from the treatment of mesenchymal malignant neoplasms with a fibroblast-inhibiting agent such as chloroquine, based on the unique idea of ours. 1) One of 3 cases of lymphosarcoma showed a complete remission. 2) All the 3 cases of giant follicular lymphoma showed a diminution of lymph nodes, and they were thought to be almost in a complete remission. 3) One case of fibrosarcoma showed a diminution and necrosis of tumors. 4) No effect of chloroquine was observed in such case as reticulum cell sarcoma, Hodgkin's disease and synovial sarcoma. 5) Lymph node diminution was observed in acute and chronic lynphocytic leukemias, but they did not reach to a complete remission. 6) One of 4 cases of chronic myelogenous leukemia showed a reduction of hepatosplenomegaly, a decrease of white blood cell counts associated with hematological improvement, but it did reach to a complete remission. 7) Side effects of chloroquine were observed in 6 of 24 cases, and included slight gastrointestinal symptoms. However, they were alleviated by either discontinuance or dose decrease of chloroquine. Since severe side effects such as retinopathy have been reported, periodical ophthalmological examination is necessary.