To elucidate the initial pathogenic events in lymphoid organs, the major reservoir of virus in HIV infection, follow-up of viral load and cytokine mRNA production was performed in the rhesus macaque SIV mac251 model. In the first experiment, lymph nodes (LN) obtained from animals sacrificed at early time points following intravenous (i.v.) inoculation with a high viral dose, showed that the production of cytokine mRNA in LN (IFN gamma, IL1 beta, IL2, IL4, IL12p40, IL6, IL10, TNF alpha and TNF beta) was correlated with viral replication and persisted during the two months post-inoculation (p.i.). In the second experiment, LN were sequentially analysed in two groups of animals receiving i.v. a high or a low viral dose. The initial higher local production of IFN gamma mRNA in LN was associated with weak viraemia, the capacity of the host to decrease productive infection in LN measured at one and two months p.i., and slow disease progression.