Although it has been well documented that drugs of abuse such as cocaine cause enhanced progression of human immunodeficiency virus (HIV)-associated neuropathological disorders, the underlying mechanisms mediating these effects remain poorly understood. The present study demonstrated that exposure of rat primary neurons to both cocaine and gp120 resulted in increased cell toxicity compared to cells treated with either factor alone. The combinatorial toxicity of cocaine and gp120 was accompanied by an increase in both caspase-3 activity and expression of the proapoptotic protein Bax. Furthermore, increased neurotoxicity in the presence of both the agents was associated with a concomitant increase in the production of intracellular reactive oxygen species and loss of mitochondrial membrane potential. Increased neurotoxicity mediated by cocaine and gp120 was ameliorated by NADPH oxidase inhibitor apocynin, thus underscoring the role of oxidative stress in this cooperation. Signaling pathways including c-jun N-teminal kinase (JNK), p38, extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinases (MAPK), and nuclear factor (NF)-kappaB were also identified to be critical in the neurotoxicity induced by cocaine and gp120. These findings thus underscore the role of oxidative stress, mitochondrial and MAPK signal pathways in cocaine and HIV gp120-mediated neurotoxicity.