Human immunodeficiency virus (HIV) infection produces a profound impairment of immune functions that antiretroviral therapy is unable to restore. Because of its immuno-enhancing properties, interleukin 2 (IL-2) has been used as a therapeutic tool in HIV+ subjects. IL-2 produces an increase of CD4 and CD8 lymphocyte absolute counts that is preferentially due to the expansion of the ?naive? cells. In addition, IL-2 increases cytokine production from the cells of the immune system and is able to up-regulate the expression of cytokine receptors, such as the chemokine receptors CCR-5 and CXCR-4. Less informations on the IL-2 activity on the CD8 subset are available at the moment. The advent of highly active antiretroviral therapy has changed this scenario, making the IL-2 effects less clear-cut than previously hypothesized. We suggest that the ongoing studies will define the precise role of IL-2 in the therapy of HIV infection.