We examined the in vitro anti-human immunodeficiency virus (HIV) activity of MRN-100, an iron-based compound derived from bivalent and tervalent ferrates. MRN-100 action against HIV-1 (SF strain) was tested in primary cultures of peripheral blood mononuclear cells (MNC) by analyzing p24 antigen production and percent survival of MNC infected with HIV. MRN-100 at a concentration of 10% (v/v) inhibited HIV-1 replication in 11 out of 14 samples (79%). The percentage of suppression of p24 antigen was ？12.3 to 100% at 10 days post-treatment. MRN-100 also exhibited a significant protective effect in the survival of HIV-1-infected MNC. MNC survival post-treatment was dose dependent, 70.4% ± 8.4, 83.6% ± 10.7 and 90% ± 11.4, at concentrations 2.5, 5 and 10% (v/v), respectively, as compared with 53% ± 4 for HIV-1-infected MNC without treatment. The effect was detected as early as 4 days and continued up to 11 days. Treatment with MRN-100 caused no significant change in proliferative response of MNC alone or cocultured with different mitogens: PHA and Con-A (activators of T cell function) and PWM (activator of CD4+ T cell-dependent B cells). We concluded that MRN-100 possesses anti-HIV activity in vitro and without an increase in lymphocyte proliferation, MRN-100 may be a useful agent for treating patients with acquired immunodeficiency syndrome.