Serial determinations of serum α(1)-acid glycoprotein (α(1)-AG) and α(1)-antitrypsin (α(1)-AT) were performed in 43 cases with lung cancer and 25 cases with stomach cancer during therapeutic procedures, and in 31 courses of remission induction-chemotherapies of 23 cases with malignant lymphoma. These studies reveal that changes in serum α(1)-AG levels during chemotherapy would be an index to the efficacy of chemotherapeutic agents for malignant neoplasms because it has been shown that α(1)-AG levels changed in intimate relation to neoplastic processes in almost all the cases of lung or stomach cancer. Especially, in malignant lymphoma, changes in α(1)-AG levels during the clinical course showed such a close relation to vicissitudes of lymphadenopathy that serial determinations of this glycoprotein was regarded as a reliable index not only for the efficacy of chemotherapy but also for the early detection of relapse prior to the manifestations of clinical symptoms. On the other hand, changes in α(1)-AT levels did not correlate to the progression of canecrous lesions in almost half the cases recieving various chemotherapeutic agents and corticosteroids. It was considered that these agents, especially corticosteroids, might be directly concerned with metabolism of this glycoprotein. In patients with lung or stomach cancer who did not obtain any clinical improvement during chemotherapy, significant correlation was observed between α(1)-AG as well as α(1)-AT levels prior to chemotherapy and their life spans. Therefore, it was possible to set up a regression line of life spans against these glycoprotein levels and life spans of ineffective cases to chemotherapy could be estimated roughly according to this regression line.