The chronically HIV-infected cellular reservoir in lymphoid tissue (LT) represents a formidable obstacle to the long-term success of antiretroviral therapy. Cytoreductive chemotherapy with cyclophosphamide (CTX) reduces cells in LT, and we hypothesized that coadministration of antiretroviral therapy with CTX may diminish the cellular reservoir over time. Ten antiretroviral treatment-naive subjects were recruited, and they received stavudine, lamivudine and nelfinavir (antiretroviral therapy, ART) until 2 consecutive plasma HIV RNA levels measured < 50 copies/ml (step 1). Five subjects then received ART alone, whereas five subjects received ART plus three escalating doses of CTX (step 2). Viral DNA was measured in LT obtained by excisional lymph node biopsy and peripheral blood mononuclear cells (PBMCs), using quantitative polymerase chain reaction at three time points in both groups (before steps 1 and 2, and after CTX). Viral DNA declined in both groups after the initiation of ART alone in step 1. During step 2 both groups experienced a modest decline compared with step 1. However, no significant differences were observed in viral DNA in LT or PBMCs between the ART alone and the ART plus CTX groups. Suppression of plasma HIV RNA levels < 50 copies/ml was not maintained in the ART plus CTX group, perhaps because of inadequate medication adherence. The group receiving ART plus CTX had lower CD4(+) lymphocyte counts and absolute total lymphocytes compared with the ART alone group. We conclude that the addition of CTX to ART did not diminish the cellular reservoir in HIV-infected persons.