Interleukin-2 (IL-2) is a glycoprotein with significant immune effects. Our aims in this study were to define the early immune response of low-dose IL-2 therapy in patients with metastatic malignant melanoma. Ten patients with metastatic malignant melanoma with no prior therapy and 10 healthy persons as a control group were included in the study. IL-2 (4.5 Mio U/day) was injected subcutaneously from day I to day 4 (D1-4) to the patients. It was found that the absolute values of cluster of differentiation (CD)2, CD3, CD4 and CD8 T-cells increased significantly on day 5 (p=0.03, p=0.03, p=0.02, p=0.003, respectively). CD 16/CD56 positive natural killer cells increased significantly at h 24 (p=0.008). IL-2 receptor (CD25) expression on CD2 positive, and human leukocyte antigen (HLA)-DR expression on CD3 positive T-cells increased markedly on the 5th day of treatment (p=0.01, p=0.05, respectively). Memory T-helper cells (CD4/CD45RO) showed a significant increase on day 5 (p=0.03). In conclusion, low-dose subcutaneous consecutive-day administration of IL-2 leads to early and effective immunostimulation in patients with metastatic melanoma.