1 x 10(5) cells of FAMFT-induced bladder cancer cell line (MBT-2) were injected into the right leg of the C3H/He mice. 10 days later, these animals with the same tumor size were divided into four groups. Group 1 is the control with no treatment. Group 2 underwent interleukin 2 (IL-2) treatment for 10 days since the 11th day after tumor inoculation. Group 3 received just one CPM injection on the 10th day. Group 4 had a combination therapy of CPM, followed by IL-2. Group 1 and 2 exhibited enlargement of tumor size, resulting in the death of all animals. Administration of CPM led to temporary disappearance of tumor, followed by local tumor recurrence in all cases. However, combined therapy with IL-2 showed complete remission of the tumors. Natural killer cell activity measured by the 51Cr release assay of the spleen cells using Yac-1 cells as target cells 20 days after tumor inoculation was found to be significantly higher in group 2 and 4, while lymphokine-activated killer cell activity of the spleen cells against P-815 cells showed no significant difference between the four groups.