The transforming growth factor-beta family of polypeptides includes three related isoforms with pervasive effects on immune system function. In this study, the authors evaluated human brains with human immunodeficiency virus (HIV)-1 encephalitis for transforming growth factor beta (TGFbeta)1, TGFbeta2, and TGFbeta3 immunoreactivity using isoform-specific polyclonal antibodies and avidin-biotin immunohistochemistry. Normal brains and those with progressive multifocal leukoencephalopathy, toxoplasma encephalitis, and cryptococcal meningitis were used as controls. In normal controls, TGFbeta1, TGFbeta2, and TGFbeta3 immunoreactivity were confined to arachnoid cells and blood vessels. In 9 of 10 cases of HIV-1 encephalitis, all three isoforms were also detected in arachnoid cells. In addition, variable, predominantly TGFbeta2 and TGFbeta3 immunoreactivity were also detected in reactive astrocytes and mononuclear cells of white matter lesions. Extensive TGFbeta3 immunoreactivity was also detected in multinucleated giant cells in one case. In a case of cryptococcal meningitis, all three isoforms were detected in arachnoid cells and macrophages. Lesions of progressive multifocal leukoencephalopathy and toxoplasma encephalitis also exhibited TGFbeta1, TGFbeta2, and TGFbeta3 immunostaining in reactive astrocytes. These findings suggest that TGFbeta isoforms are present in HIV-1 encephalitis and may participate in the pathogenesis of this and other inflammatory central nervous system (CNS) lesions associated with acquired immunodeficiency syndrome (AIDS).