The in vivo response of the immune system after HIV infection in regard to cytokine production and C-C chemokine synthesis is not well known. Here we have analysed cytokine and chemokine mRNA production in lymph nodes with follicular hyperplasia (FHLN) of HIV-infected patients byin situ hybridization using anti-sense mRNA probes. The synthesis of mRNAs for interferon-gamma (IFN-γ), IL-12p35, IL-12p40, IL-4, and for the C-C chemokines RANTES, MIP-1α, and MIP-1β was compared with that of lymph nodes from non-infected individuals to define HIV-specific events. Only few cells expressing IFN-γ, RANTES, MIP-1α, and MIP-1β mRNAs were detectable in the T-dependent area of lymph nodes from HIV-negatives. In contrast, in FHLN from HIV+ patients a high number of IFN-γ, RANTES, MIP-1α, and MIP-1β mRNA-containing cells were detectable. Remarkably, only single individual IL-12p35 mRNA-producing cells were present in the T-dependent area from both HIV+ and HIV- lymph nodes. Furthermore, the low number of IL-12p40 mRNA-expressing cells did not differ between HIV+ and HIV- lymph nodes. This indicates that IFN-γ is expressed independently of IL-12, possibly by a direct T cell-mediated reaction. IL-4 mRNA-producing cells were hardly detectable in infected and control lymph nodes. The same findings were made in a limited number of samples from patients with advanced disease. Thus, these results demonstrate that a high IFN-γ production is accompanied by a strong expression of MIP-1α, MIP-1β, and RANTES in the lymph node after HIV infection. This favours the idea that a Th1-type immune response correlates with a preferential production of C-C chemokines in FHLN of HIV+ patients.