We have previously reported on the assembly of recombinant human immunodeficiency virus (HIV)-like particles that contain gag structural proteins and present env glycoproteins gp120 and gp41 on their surfaces (O. Haffar,. J. Garriques, B. Travis, P. Moran, J. Zarling, and S.-L. Hu, J. Virol. 64:2653-2659, 1990). On the basis of their structures, we hypothesized that the recombinant particles would interfere with virus infection and tested our hypothesis in vitro by using peripheral blood mononuclear cells (PBMC) from HIV type 1-seropositive donors. Addition of the recombinant particles to PBMC concomitant with stimulation by anti-CD3 inhibited virus production, as determined by reduced levels of p24 in the culture supernatants. This inhibition of p24 production correlated with lower levels of cell-associated viral DNA. Several lines of evidence suggested that the recombinant particles exerted their antiviral effects primarily by inhibiting virus production from latently infected cells and not by inhibiting subsequent virus spread. Importantly, CD4+ T-cell stimulation by specific antigen or by anti-CD3 was not inhibited by treatment with the recombinant particles. This apparent selective inhibition of virus replication in infected PBMC represents a novel property of the recombinant HIV-like particles.