Pilot studies have suggested that treatment with recombinant human growth hormone (rhGH) is associated with increased T-lymphocyte restoration and enhanced thymic output. We evaluated the immunologic effects of rhGH on HIV(+) subjects with incomplete immune reconstitution on antiretroviral therapy (ART). Sixty subjects were randomized to receive rhGH 1.5 mg scqd and ART for 48 weeks (Arm A) or continue ART alone for 24 weeks then add rhGH 3.0 mg scqd for 24 weeks (Arm B). Median baseline CD4 for Arms A and B were 223 and 219, respectively. There was little difference between Arm A and Arm B in change in total or naive CD4 cells or percentage from baseline to week 24. Only one subject in Arm A met the primary endpoint, an increase in naive CD4 percentage of at least 10 percentage points. By week 48 both Arms had statistically significant increases in naive CD4 cell count and percentage and thymus size. Within Arm B, treatment with rhGH was associated with significant increases in naive CD4(+) cell count and percentage compared with ART alone. Treatment with rhGH +ART may be associated with modest increases in CD4 lymphocytes over ART alone in subjects with CD4 <350, yet the origin of these naive cells and their impact on immune function require further investigation.