The biological significance of soluble IL-2 receptors (sIL-2R) is still unknown; in particular, it is not yet clear whether their increase in the blood may reflect activation of immune cells, or whether it is related to an immune dysfunction. To investigate this problem, we evaluated serum levels of sIL-2R before and after administration of a highly lymphocytolitic chemotherapy (FEC: fluorouracil, epirubicin, cyclophosphamide) in a group of 6 patients with advanced breast cancer. SIL-2R were analyzed in relation to lymphocyte number. Absolute mean number of lymphocytes was significantly lower after than before chemotherapy. On the contrary, no significant difference was seen in sIL-2R mean levels, and no significant correlation was observed between changes in sIL-2R and in lymphocyte number following chemotherapy. These results would exclude that sIL-2R may simply be due to a passive release following lymphocytic damage.