Serum soluble Interleukin-2 receptor levels (sIL-2R) were measured in 121 patients (pts) with non-Hodgkin's lymphoma (NHL) and in 30 patients with Chronic lymphocytic leukemia (CLL). Sera collected from 32 normal volunteers and 18 patients with infection or a variety of non malignant hematological disorders served as controls. A small number of patients with Hairy cell leukemia (HCL) and Hodgkin's disease (HD) were also studied. NHL patients were classified according to their clinical status as "active" (82 pts) or "non-active" (39 pts) and CLL according to the stage of their disease. NHL patients were also further classified as low (55 pts), intermediate (38 pts) and high grade malignancy (28 pts), according to the Working formulation scheme. A significant difference was found between the high levels of sIL-2R in patients with "active" disease and the lower levels in patients with quiescent or responsive disease. Significantly different high levels were found in patients with aggressive (intermediate and high grade) lymphoma as opposed to low grade lymphoma and CLL. In CLL itself higher levels of sIL-2R were seen in more advanced disease than in early disease. Thirteen patients with active Hodgkin's disease (HD) had moderately elevated sIL-2R levels, similar to those recorded for patients with infections and some non-malignant hematological disorders while another 13 HD patients in remission, had normal levels comparable to those recorded in normal controls. Extremely high levels of sIL-2R were seen in 2 patients with HD with severe viral infections and levels approaching those seen in HCL, were noted (20-30,000 u/ml).(ABSTRACT TRUNCATED AT 250 WORDS)