To investigate serum interleukin-2 (IL-2) and soluble interleukin-2 receptor (SIL-2) levels in gestational trophoblastic diseases (GTD).Sixty-six patients with GTDs and 23 first-trimester healthy pregnant women (controls) participated in this study. According to the World Health Organization scoring system, GTDs were subgrouped into the following groups: 30 hydatidiform mole spontaneous regression (HMSR), 12 postmolar gestational trophoblastic tumors of high risk (PMHR), 14 low-risk choriocarcinomas, and ten high-risk choriocarcinomas. Before treatment, a blood sample from each case was assayed for beta-hCG by radioimmunoassay, IL-2 by IRMA, and SIL-2R by enzyme-linked immunosorbent assay. Follow-up beta-hCG assays were carried out at weekly intervals after treatment for 3 months, then monthly for 1 year.Serum IL-2 levels in all subgroups of GTD were significantly lower than that of controls. Meanwhile, there were concomitant significant elevations of serum SIL-2R, showing mean rises of 3.86-fold, 3.9-fold, twofold, and 6.1-fold for cases of HMSR, PMHR, low-risk choriocarcinoma, and high-risk carcinoma, respectively. All cases of high-risk choriocarcinoma revealed abnormally high SIL-2R values. There was a significant positive correlation between serum beta-hCG and SIL-2R concentrations.The possible causes of IL-2 decreases and SIL-2R increases may indicate a defective immune response in GTDs. The high correlation between SIL-2R level and tumor burden suggests the use of serum SIL-2R assay for disease monitoring: SIL-2R is indirect marker of tumor activity, and it is useful in the differential diagnosis of GTD because a normal value of serum SIL-2R excludes high-risk cases of choriocarcinoma.