Immunological studies of the peripheral blood were made in terminal breast cancer and terminal abdominal cancer patients. Two immunological parameters were studied: (1) lymphocyte subsets and (2) proliferative response to PHA. A decrease in the number of OKT-3(+) cells and an increase in that of OKT-8(+) cells were observed in abdominal cancer. It was suggested that the immunological status in abdominal cancer is more suppressive than in breast cancer. Increases in the number of OK-M1(+) cells and Leu-7(+) cells were observed in breast cancer. It is suggested that cytotoxic lymphocytes increase in number in breast cancer more than in abdominal cancer.