Little is known about the influence of CSFV infection on cell-mediated immune responses. In a preliminary study, we have determined by a quantitative RT-PCR, the production of IFNy and IL4 mRNA in PBMC collected from naive or recovering infected pigs. PBMC were re-stimulated in vitro for two days with the infectious virus before mRNA quantification. We have also evaluated the CSFV-specific proliferative responses of PBMC by the analysis of BRDU incorporation in cell DNA by flow cytometry. After in vitro restimulation with virulent CSFV, a high level of IFNy mRNA expression was detected in PBMC from immune pigs whereas a low level of IL4 mRNA was observed in these pigs. In contrast, none of these cytokines were observed in naive pigs. Immune pigs also developed a CSFV-specific proliferation two weeks post-infection while the response of naive pigs remained low. Characterization of PBMC subsets involved in this proliferative response is under process. Although studies showed that CSFV replication could be efficiently control by antibodies, our results suggest the development of cellular immune responses may also act in the control of the virus.