OBJECTIVE: To decrease viraemia levels in primary HIV infection by using a combination of zidovudine (ZDV) and L-697,661. DESIGN: Four primary HIV-infected patients were treated for 6 months with ZDV, 250 mg twice daily, in association with the non-nucleoside reverse transcriptase inhibitor L-697,661 500 mg three times daily. Viraemia, proviral DNA, CD4 and CD8 cell counts were measured serially during 18 months. RESULTS: Viraemia decreased to undetectable levels (< 200 RNA copies/ml) in two patients. A third patient had a marked decrease followed by a rebound during therapy; viraemia levels did not vary markedly in the fourth patient. A rebound in viraemia levels was observed within 15 days of discontinuation of therapy in the three responding patients. Proviral levels evolved in parallel with viraemia but were always detectable in all patients. In the three patients with an initial decrease of viraemia, CD4 cell counts were within the normal range 2 months after initiation of therapy and did not markedly decrease after discontinuation of therapy. In the two patients with partial or no response of viraemia, mutations associated with low level of resistance to L-697,661 appeared during treatment. CONCLUSION: A marked decrease of viraemia can be achieved in some primary HIV-infected patients with combined therapy. Six months of treatment does not prevent a rebound of viraemia, which was observed within 15 days of interruption of therapy.