This paper described T cell proliferative response by an alternative pathway in normal subjects and In patients with malignant diseases. Two McAbs, Anti-CCTl and Lo-CD2-act recognizing two distinct epitopes on E-receptor (CD2) were used to costimulate PBMC. Proliferative responsiveness was measured by 3H-thymidine incorporation. It was found that 82% of 72 nonnal subjects gave proliferative response whereas only 23% of the 93 patients did. The average cpm±SD in patients with bladder cancer (118±2314), kidney cancer (1619±2719) or lymphoma (2518±4057) was significantly lower than that in normal subjects (4935±2314), (P<0.001). These results indicate that T cell proliferation through the alternative pathway was significantly depressed in patients with cancer, and this can be used as a new parameter to monitor the immune status of cancer patients. Two McAbs, Anti-CCTl and Lo-CD2-act recognizing two distinct epitopes on E-receptor (CD2) were used to costimulate PBMC. This paper described T cell proliferative response by an alternative pathway in normal subjects and In patients with significant diseases. Proliferative responsiveness was measured by 3H-thymidine incorporation. It was found that 82% of 72 nonnal subjects gave proliferative response because only 23% of the 93 patients did. The average cpm±SD in patients with bladder cancer (118±2314), kidney Cancer (1619±2719) or lymphoma (2518±4057) was significantly lower than that in normal subjects (4935±2314), (P<0.001). These results indicate that T cell proliferation through the alternative pathway was significantly depressed in patients with Cancer, and this can be used as a new parameter to monitor the immune status of cancer patients.