We serially measured the serum levels of soluble interleukin-2 receptor (sIL-2R) and soluble CD8 (sCD8) in 36 patients with malignant lymphoma (33 non-Hodgkin's lymphoma cases and three Hodgkin's disease cases). The level of serum sIL-2R was significantly elevated in patients with active disease (18) compared to those in remission (18), and correlated with the clinical stage of the lymphoma. The temporal profile of the sIL-2R level reliably represented the disease status, which was judged clinically, during the course of the disease. In three patients, the tumor bulk paralleled the sIL-2R level. On the other hand, a less significant correlation was found between the serum sCD8 level and disease activity. The serial measurement of sCD8 appeared to be less useful for monitoring the disease activity, although there was a significant correlation between the sCD8 and sIL-2R levels. This study indicates that serial measurement of the serum sIL-2R level may be useful for monitoring the tumor burden in response to treatment and for early detection of disease progression in malignant lymphoma.