Secretory products from HIV-1-infected immune-competent mononuclear phagocytes (MP) damage neuronal dendritic arbor (Zheng et al., 2001). The mechanism behind neuronal injury and whether it is species and/or viral strain dependent is not fully understood. To these ends, we investigated whether HIV-1-infected and lipopolysachharide (LPS)-activated MDM elicit neuronal injury in primary human neurons. Neuronal damage was compared to that seen in rat neurons. Utilizing a spectrum of HIV-1 strains to infect human monocyte-derived macrophages (MDM), productive viral replication proved necessary, but not sufficient, for neuronal injury. Neuronal demise was induced by virion-free HIV-1-infected and immune-activated MDM culture supernatants. Maximal alterations in glutamate mediated neuronal signaling, resulted from exposure to secretory products from HIV-1-infected and immune-activated MDM. Apoptosis was the predominant mechanism of cell death induced by HIV-1-infected and LPS-treated MDM. Importantly, neuronal injury and increases in calcium influx mediated by HIV-1-infected and immune-activated MDM culture supernatants was partially blocked by the N-methyl D-aspartate (NMDA) receptor antagonist, MK 801. These data support a primary role for immune-activation in MP neurotoxic activities. The upregulation of NMDA receptor sensitive soluble factors and neuronal apoptosis by HIV-1-infected and immune-activated MDM provide unique insights into links between soluble factors, produced as a consequence of MP immunity, and neuronal demise in HAD.