Human immunodeficiency virus (HIV) infection of the brain leads to massive neuronal damage, resulting in the AIDS (acquired immunodeficiency syndrome) dementia complex (ADC). A recent study using transgenic mice indicates that neurons possess transcription factors capable of activating the HIV promoter. To identify these, we transfected two types of primary cultures of rat neurons with HIV promoter-reporter gene constructs. The two kappa B regulatory sites in the HIV long terminal repeat (LTR) are shown to be essential for strong promoter activity. Two proteins present in neurons, BETA and an NF-kappa B-like protein, can bind the kappa B sites. These proteins are shown to belong to distinct families of transcription factors. Mutation analysis and transfection of a dominant negative NF-kappa B mutant, indicate that the neuronal NF-kappa B-like activity mediates HIV promoter activation. cDNA cloning, biochemical and immunological analyses indicate that neuronal NF-kappa B is similar to NF-kappa B of other tissues. Transfections of primary neuron cultures with an HIV promoter-beta-galactosidase construct show that within these cultures, neurons are indeed the cells that highly activate the HIV promoter. Thus, analogous to the situation in T-lymphocytes and macrophages, NF-kappa B is an activator of HIV transcription in neurons.