Microglia become activated in a wide range of neurodegenerative disorders, including Alzheimer's disease. Such activation may lead to autodestruction of neurons. It is demonstrated here that activation of both human microglia and monocytic THP-1 cells by a combination of lipopolysaccharide and interferon-gamma results in secretion of neurotoxins that kill human neuronal SH-SY5Y cells. This neurotoxicity can be partially blocked by inhibitors of cytosolic phospholipase A2, cGMP-selective phosphodiesterases, or protein kinase C. When combinations of these inhibitors, or combinations of an inhibitor plus nordihydroguaiaretic acid, or the nonsteroidal anti-inflammatory drug diclofenac were tried, additive reductions in neurotoxicity were observed. It is concluded that the stimulants activated multiple intracellular pathways, and that combination therapies inhibiting these pathways might be beneficial for treating neurodegenerative disorders.