High-dose chemotherapy in conjunction with bone marrow transplantation (BMT) or peripheral blood stem cell transplantation (PBSCT) is increasingly being used for treatment of patients with hematological malignancies. Residual tumor cells, resistant to high-dose chemoradiotherapy, are responsible for reccurence of the disease. Interleukin 2 (IL-2), a pleiotropic cytokine which plays a central role in immune response, has been introduced in several clinical trials in patients with hematological malignancies after BMT or PBSCT to increase immunocompetence of these patients and eradicate residual malignant cells. At present there is no general agreement on the optimum dosage or route of administration and clinical trials also gave conflicting results. Establishment of optimum dosage schedules and methods of administration should enable a better assessment of the place of IL-2 in the treatment of these patients.