This study was undertaken to determine if advanced epithelial ovarian cancer was associated with increased serum and ascitic levels of soluble interleukin-2 receptor alpha (sIL-2R alpha). Serum and ascitic fluid samples from 23 ovarian cancer patients were analyzed for sIL-2R alpha using an enzyme-linked immunosorbent assay and compared with the serum and peritoneal levels in 18 normal females. The samples were analyzed for CA-125 levels using a radioimmunoassay and the total protein was also measured. Normal individuals had low serum levels of sIL-2R alpha (367.5 +/- 44.6 U/mL), with similar levels of sIL-2R alpha in the normal peritoneal fluid (438.6 +/- 48.8 U/mL). In contrast, the serum and ascitic fluid levels in ovarian cancer patients were significantly higher (746.7 +/- 82.9 U/mL, P = .0006; 2,656.7 +/- 373.7 U/mL, P = .00002, respectively). The results for sIL-2R alpha were also significant when the levels were expressed per milligram of total protein. More importantly, in almost every ovarian cancer patient the ascitic sIL-2R alpha level far exceeded the serum level, a pattern also observed for CA-125. There was no correlation between the serum and ascitic sIL-2R alpha levels, or between the serum and ascitic CA-125 levels. Although the serum levels of sIL-2R alpha and CA-125 were elevated in the same patient, overall there was no correlation between the serum sIL-2R alpha and serum CA-125 levels, either when the levels were expressed in absolute units or per milligram of total protein. Similarly, there was no correlation between sIL-2R alpha and CA-125 levels in individual ascitic samples. While CA-125 levels may reflect an independent index of tumor burden, these results suggest that selective accumulation of sIL-2R alpha in the ascites may be one of the factors associated with the known nonresponsiveness of the infiltrating lymphocytes against ovarian carcinoma cells.