Activated lymphocytes can release a soluble form of IL-2 receptor (sIL-2R), which retains the capacity to bind IL-2. Abnormally high values of sIL-2R have been observed in patients with advanced solid tumors. In an attempt to further understand the biological significance of sIL-2R in solid tumors, this study investigated the relation between sIL-2R and Tac-positive cells. sIL-2R serum levels and Tac-positive cells were determined in 18 patients with solid tumors metastatic, 108 non-metastatic. Tumor types were: breast 7; lung 6; colon 2; stomach 1; testis 1; larynx 1. No correlation was found between circulating sIL-2R values and Tac-positive cells, and there was no difference between Tac-positive cell mean number in patients with high and normal sIL-2R levels. These preliminary results suggest that different mechanisms are responsible for sIL-2R release in the blood and IL-2 receptor expression on the immune cell surface.