Twenty-two patients with CD4(+)cell counts <or=200 cells/microL after 12 months of stable highly active antiretroviral therapy (HAART; "immunologic nonresponders") were randomly assigned to receive subcutaneous low-dose prolonged intermittent interleukin (IL)-2 in addition to HAART (n=12) or to continue HAART alone (n=10). At 48 weeks of follow-up, no IL-2-related serious adverse events and no significant differences in plasma human immunodeficiency virus (HIV) RNA level were observed in the 2 groups. A higher incidence of HIV-related clinical events was observed among patients receiving HAART alone (3/10) than among subjects receiving HAART plus IL-2 (0/12). Significant increases in CD4(+), naive, and CD4(+)CD7(+) cells and plasma levels of IL-7 were observed in patients receiving IL-2 versus patients receiving HAART alone. A significant increase in cell turnover did not lead to a decrease in the frequency of T cell receptor excision circles, which remained stable. Rather, increased numbers of T cell receptor excision circles per microliter of blood were observed (not statistically significant). Thus, adjuvant IL-2 therapy in immunologic nonresponders resulted in a clinical benefit, suggesting that the quantitative cell recovery involves functionally competent immune cells.