Objective of the present study was then to assess the antiviral activity of the protease inhibitor amprenavir in macrophages (M/M), and to compare it with its efficacy in peripheral blood lymphocytes (PBL). M/M were obtained from blood of sero-negative healthy donors and infected with M-tropic HIV-1 strain (HIV-1(Ba-L)). The stabilized infection was assessed by monitoring the HIV-1 p24 gag antigen production in the supernatants of M/M cultures. In the setting of acute infection (treatment before HIV-1 challenge), amprenavir showed substantial activity both in M/M and PBL at similar concentrations (EC(50): 0.011 and 0.031 microM, respectively); complete inhibition of HIV-1 replication was achieved in both cell types at concentration of about 2 microM. In the setting of chronical infection (i.e. antiviral treatment several days after established infection), an antiviral effect of amprenavir was achieved in M/M, but at concentrations higher than those active in acutely infected M/M (EC(50): 0.72 microM, EC(90): 18.2 microM). The antiviral effect in chronically infected M/M was sustained for at least 2 weeks of continuous treatment. These findings suggest that amprenavir (at relatively high concentrations) has a clinically relevant antiviral effect in persistently infected reservoirs of HIV.