To assess the hypothesis that the plasma soluble interleukin-2 receptor (sIL-2R) level may have predictive value for morbidity/mortality in patients with myelodysplastic syndromes (MDS), we determined in plasma sIL-2R level of 80 MDS patients and examined their subsequent clinical course. Compared with low-risk MDS (refractory anaemia (RA) and RA with ringed sideroblasts) patients and normal subjects, the plasma sIL-2R level was significantly elevated in high-risk MDS (three other MDS subtypes and acute leukaemia following MDS) patients (high-risk MDS versus low-risk MDS, P < 0.01; high-risk MDS versus normal subjects, P < 0.01). 14/40 low-risk MDS patients developed at least one of the following during the follow-up period: erythrocyte transfusion dependence, infections requiring hospitalization, disease progression or MDS-related death. The plasma sIL-2R level was higher in these eventful subjects than in event-free low-risk subjects (P < 0.0001), and all of 10 low-risk subjects with a plasma sIL-2R level > 540 U/ml experience at least one event. By logistic regression analysis of various parameters in these 40 low-risk subjects, the plasma sIL-2R level was identified as the strongest independent parameter for predicting eventful subjects (P < 0.0047). The plasma sIL-2R level did not show a predictive value in high-risk MDS. This study revealed that the plasma sIL-2R level is significantly elevated in high-risk MDS and suggested that the plasma sIL-2R level is a valuable predictive factors for the clinical outcome in low-risk MDS.