Hairy cell leukemia (HCL) is a chronic lymphoproliferative disorder of the B cell lineage. In the search for specific markers with prognostic significance we evaluated the clinical value of IL-1 beta and sIL-2R levels in HCL patients. HCL patients (25) were classified according to their clinical status as "active", "non active" disease or partial or complete remission and response treatment. We found a good correlation between IL-1 beta or IL-2R levels and disease activity: improved clinical status or response to different therapies were associated with decreasing IL-1 beta or sIL-2R levels. In contrast, lack of response to therapy or disease progression was reflected in increases in both IL-1 beta and sIL-2R levels. In some patients increases of both cytokines preceded clinical symptoms. In conclusion our results show that IL-1 beta and s-IL-2R levels may be used as reliable markers for monitoring HCL activity, assessing response to treatment and predicting early progression of disease.