Objective:To assess the antiretroviral effect of a combination of zidovudine, didanosine, lamivudine and saquinavir in plasma, peripheral blood mononuclear cells (PBMC) and lymph-node mononuclear cells (LNMC) after 8 weeks.Methods:Ten HIV-1 antiretroviral therapy-naive patients were given a combination of oral zidovudine (200 mg three times daily), oral didanosine (200 twice a day), oral lamivudine (150 mg twice a day) and oral saquinavir (600 mg three times daily). HIV-1 plasma RNA was measured by quantitative reverse transcriptase (RT)-polymerase chain reaction (PCR). Infectious HIV-1 in PBMC and LNMC was measured by a coculture technique. HIV-1 RNA in PBMC and LNMC was quantified by RT-PCR. Proviral DNA titres in PBMC and LNMC were measured by endpoint dilution PCR. CD4 T-cells were analysed by flow cytometry.Results:CD4 cell counts rose in all patients (mean increase of 125 ± 71 CD4 cells × 106/l) and the benefit was greater for patients with fewer than 350 CD4 cells × 106/l (mean increase of 159 ± 74 CD4 cells × 106/l). Plasma HIV-1 RNA decreased exponentially in all patients (mean decrease of 3.1 log10after 8 weeks with a mean half-life of 2.2 ± 0.6 days). HIV-1 RNA showed a decrease of 3.07 log10in PBMC and of 2.1 log10in LNMC. The decrease in plasma HIV-1 RNA was consistently associated with the decrease in LNMC. These data were supported by a concomitant drop of HIV-1 infectious titres in PBMC (mean decrease of 1.41 log10) and in LNMC (mean decrease of 2.54 log).Conclusions:These data show a significant antiretroviral effect of this four-drug combination in blood and lymphoid tissues. However, a greater decrease in HIV-1 RNA was observed in PBMC and in plasma than in lymph node cells.