The aim of the present study was to assess the prognostic value of soluble interleukin-2 receptor (sIL-2R) serum levels in stage I-III melanoma patients. The levels of sIL-2R were determined using an enzyme immunometric test kit in 329 patients affected by malignant melanoma (MM) from 1995 to 2004. Correlations between sIL-2R values, baseline patients and tumour features were studied by contingency tables and the chi-square test. The Kaplan-Meier product limit method was applied to plot disease-free survival (DFS) curves. Univariate analysis was performed with the Log-rank test. Cox proportional-hazards regression was used to analyse the effect of several risk factors on DFS. In total, 2330 blood samples were collected during follow-up of 329 MM patients. Forty-five (13.7%) patients had Breslow tumour thickness<or=1.00, 83 (25.2%) patients>1.00 and <or=2.00 mm, 72 (21.9%) patients>2.00 and <or=4.00 mm, and 47 (14.3%) patients>4.00 mm. Ulceration was present in 64 cases (19.4%). Thirty-nine sentinel lymph nodes (SLNs) (11.8%) were infiltrated by MM. Soluble IL-2R values ranged from 130 to 1420 U/ml; median value was 500 U/ml. One hundred twenty-one (36.8%) patients presented with sIL-2R>600 U/ml at first measure (FM), 194 patients (58.9%) with values increasing up to or more than 600 U/ml [increasing values (IV) pattern]. A correlation was found between Breslow's tumour values and the IV sIL-2R pattern group (P=0.0304 with chi2 test). Gender, presence of ulceration, Breslow tumour thickness, FM and IV sIL-2R pattern groups had a significant prognostic value for DFS. At multivariate analysis, presence of ulceration, gender, FM and IV sIL-2R pattern groups emerged as independent prognostic factors for DFS. The 5-year DFS rate was 88% for patients with FM<600 U/ml and 76.9% for patients with FM>600 U/ml. In IV pattern, the 5-year DFS rate was 69.5% compared to 87% for patients with no sIL-2R values>600 U/ml during follow-up. sIL-2R values are associated with progression of MM. Further studies are needed to address the role of the IL-2/IL-2R/sIL-2R axis in melanoma biology.