HIV-1 infection and nicotine addiction are global public health crises. In the central nervous system, HIV-1 causes a devastating neurodegenerative disease. It is well recognized that microglial cells play a pivotal role in the neuropathogenesis of HIV-1 and that drugs of abuse not only contribute to the spread of this agent but may facilitate viral expression in these brain macrophages. Nicotine has been shown to stimulate the production of HIV-1 by in vitro-infected alveolar macrophages, and the HIV-1 protein gp120 binds to nicotinic receptors. In this study, we demonstrated the constitutive expression of nicotinic acetylcholine receptor mRNA in primary human microglial cells and showed that the pretreatment of microglia with nicotine increased HIV-1 expression in a concentration-dependent manner, as measured by p24 antigen levels in culture supernatants. We also found that nicotine robustly altered the gene expression profile of HIV-1-infected microglia and that the transforming growth factor-beta1 is involved in the enhanced expression of HIV-1 by nicotine.