Polyclonal B cell activation is characteristic of HIV infection and occurs in the presence of severe CD4+ lymphocyte depletion. In contrast, CD4+ lymphocytes are the dominant T cell in the reactive lymphoid tissues of patients not infected with HIV. In this study, lymph node biopsies from eight HIV-infected patients with persistent generalized lymphadenopathy syndrome (PGL) were assessed for IL-1 beta, IL-2, IL-4, IL-6, IL-10, interferon-gamma (IFN-gamma) and tumour necrosis factor-beta (TNF-beta) gene expression using the polymerase chain reaction (PCR). The cytokine gene expression of two cases of reactive adenopathy in patients not infected with HIV was assessed for comparison. IFN-gamma was expressed much more strongly in the PGL samples than in control reactive lymphoid tissues, whereas the other cytokines were expressed to a similar extent in both types of tissues. IFN-gamma may have an important role in maintaining the adenopathy of HIV-infected patients. Expression of cytokines such as IL-2, IL-4 and IL-10 in HIV nodes may be adequate to allow the recruitment of naive B cells to the reactive process.