The effect of intermittent courses of recombinant interleukin-2 (rIL-2) on HIV-1 load in patients receiving combination antiretroviral therapy remains uncertain. CPCRA 059 was an open-label, randomized, multicenter trial in which 511 patients with HIV-1 infection and CD4+cell counts of ≥300/mm3who were receiving antiretroviral therapy were assigned to receive no rIL-2 (255 patients [controls]) or subcutaneous rIL-2 in dosages of 4.5 MIU (130) or 7.5 MIU (126) twice daily for 5-day courses every 8 weeks to maintain CD4+cell counts that were twice the baseline value or ≥1,000/mm3. The primary objective of this study was to compare the effects of the two doses of rIL-2 and no rIL-2 on viral load and CD4+cell counts over 12 months. There was no difference in the following viral load measurements between the rIL-2 treatment groups and the control treatment group: percentage of patients with viral loads of <50 copies/mL at 12 months (p= .55), time to viral load of ≥50 copies/mL for patients who had baseline viral loads of <50 copies/mL (p= .35), and change in viral load from baseline for patients who had viral loads of ≥50 copies/mL at baseline (p= .63). At each follow-up visit, the change in CD4+cell count from baseline was significantly greater in the rIL-2 treatment groups than in the control treatment group, with a mean difference of 251/mm3at month 12 (95% confidence interval, 207–295;p< .0001). No unanticipated adverse experiences were seen in this trial, to our knowledge the largest randomized evaluation of rIL-2 treatment conducted to date.