The aim of this study was to investigate whether Mycobacterium tuberculosis (MTB) infection affects human immunodeficiency virus (HIV) replication in T67 human astrocytoma cells and whether HIV and MTB infections induce iNOS mRNA expression in T67 cells. T67 cells were susceptible to both HIVLai and MTB infections, and MTB was able to increase HIV infection in T67 cells, as demonstrated by a marked increase in p24 release. Furthermore, both HIV and MTB infections strongly induced inducible nitric oxide synthase (iNOS) mRNA expression, as verified by RT-PCR. These findings suggest that HIV and MTB-induced iNOS expression of astroglial cells may be involved in the neuronal damage associated with HIV infection, particularly in the presence of opportunistic infections such as tuberculosis.