The association between human immunodeficiency virus (HIV) DNA load and immunologic parameters was investigated in 163 HIV-infected patients with undetectable plasma viremia during highly active antiretroviral therapy (HAART). Patients with HIV DNA below the 25th percentile (133 copies/10(6) peripheral blood mononuclear cells) had higher pre-HAART (P = 0.001) and current (P = 0.005) CD4 counts and a prolonged duration of treatment (P = 0.001). At adjusted analysis, prolonged duration of treatment was independently associated with lower (P = 0.006) and undetectable (P < 0.001) HIV DNA values.