Objectives and design:The dynamics of viral decline following the initiation of antiretroviral treatment were studied in 29 HIV-1-infected patients participating in a two-arm trial comparing immediate (group A: ritonavir, zidovudine and lamivudine) and delayed (group B: ritonavir supplemented by zidovudine and lamivudine on day 21) triple therapy. Parameters underlying viral dynamics were estimated using mathematical models tailored to these treatment protocols.Results:The decline in plasma HIV-1 density between day 0 and 21 was steeper in group A (−2.27 ± 0.46 log10) than group B (−1.87 ± 0.56 log10). In a subset of patients amenable to full mathematical analysis, a short-lived productively infected cell compartment (producing ∼97% of total virions) decayed with a half-life of 1.0–2.5 days, whereas a long-lived infected cell compartment decayed with a half-life of 18.8–32.8 days. Estimates for the time for the elimination of virus from these two cell populations ranged from 474 to 802 days. The rate of loss of productively infected CD4+ T cells was positively correlated with baseline viral load in group A and in the combined dataset.Conclusions:These results suggest that HIV-infected cell populations may have a faster turnover in patients with higher viral loads due to higher infection rate parameters, higher rates of virus production, or lower virus clearance rates.