HIV infection in brain revolves around productive viral replication in cells of mononuclear phagocyte lineage, including brain macrophages, microglia, and multinucleated giant cells [1–4]. Together, they are the instigators for cellular and viral neurotoxic activities [5–10]. Several published reports show that viral and/or cellular products produced from HIV-1-infected macrophages injure neurons and induce glial proliferation during advancing central nervous system (CNS) infection [11–18]. These findings are supported by the apparent discrepancy between the distribution and numbers of virus-infected cells and concomitant brain tissue pathology [5, 19]. Whether these soluble factors are indirectly responsible for neuronal damage remains undefined. The identification and regulation of neurotoxins produced from HIV-infected macrophages are central to uncovering how HIV mediates CNS disease. The authors who contributed to this work represent laboratories with overlapping areas of expertise. Broad-based complementary hypotheses regarding HIV neuropathogenesis are now provided. J. Leukoc. Biol. 56: 389–398; 1994.