This study presents the immunophenotypic and functional analysis of lymphocyte subsets obtained from peripheral blood and lymphoid tissue from HIV+ individuals treated with highly active anti-retroviral therapy (HAART) alone or in combination with 6 million units international (MUI) s.c. IL-2. Before treatment, the HIV+ patients had reduced CD4 and increased CD8 values in the peripheral blood and lymphoid tissue and impaired cytokine production by peripheral blood mononuclear cells (PBMC). After 24 weeks of treatment, all the HIV+ patients demonstrated increased CD4 values in peripheral blood and lymphoid tissue. The use of IL-2 did not promote an additional CD4 expansion compared with HAART alone; increased ‘naive’ and CD26+ CD4 cells and reduced CD8 cells were found in the peripheral blood and lymphoid tissue of the IL-2-treated, but not of the HAART-treated patients. Both types of treatment induced a significant reduction of the CD8/CD38+ cells. While HAART alone had negligible effects on cytokine production by PBMC, the combined use of HAART + IL-2 was unable to increase the endogenous production of IL-2, but caused an increase of IL-4, IL-13 and interferon-gamma (IFN-γ) and a reduction of monocyte chemoattractant protein-1 (MCP-1) production. These data suggest that, although in this schedule IL-2 has minimal efficacy on CD4 recovery when compared with HAART alone, it produces an increase of ‘naive’ and CD26+ CD4 cells and a partial restoration of cytokine production. These data may be used to better define clinical trials aiming to improve the IL-2-dependent immunological reconstitution of HIV-infected subjects.