In this study the authors investigated the serum levels of the released soluble form of interleukin-2 receptor (sIL-2R) in patients with non-Hodgkin's lymphomas (NHLs). Data were evaluated in relationship to the morphologic and immunophenotypic heterogeneity of NHL at diagnosis and in progressive advanced diseases. Increased sIL-2R levels were found in most cases, when compared with levels observed in healthy controls. No obvious statistical correlation has been observed between sIL-2R values in different NHL subtypes as defined by current classifications. On the other hand, major significance was related to the extent of the disease. Very high values, comparable to those observed in hairy cell leukemia, were observed in a number of large cell NHLs complicating low-grade B-cell lymphoproliferations and in a single case of T-cell Kil+ NHL. The authors' findings suggest that the detection of sIL-2R in NHL may represent a good marker in improving risk assignment of single cases and/or for monitoring remissions and exacerbations during the treatment of cases with very high levels at diagnosis. Nevertheless, the observed overlap between groups on an individual case basis can render the clinical application of this marker problematic.