Cryopreservation of animal or human peripheral blood mononuclear cells (PBMC) is a commonly used technique. Effects of cryopreservation on functional capacity, especially the cytokine production of human PBMCs, have been extensively defined. However, certain animals, such as livestock, are a shortage of these information. Here we investigated the effects of cryopreservation on cytokine (IL-4, IFNgamma and IL-6) production of porcine PBMC. The porcine PBMCs were cryopreserved at -196 degrees C for a variety time periods for 2, 5, 25 and 50 days. Viability and cytokine production of the porcine PBMCs were measured before and after cryopreservation. The results showed that about 90% cell recovery rate was obtained at each storage time, indicating that about 10% loss of PBMCs in this short-term cryopreservation was due to the freezing process rather than the duration of cryopreservation. The fresh or frozen resting porcine PBMCs produced little cytokines in the absence of stimulation. However, three cytokines were apparently increased after PMA stimulation in both fresh and frozen porcine PBMCs. The sensitivity of frozen cells to PMA simulation for IFNgamma and IL-6 production was different from that of the fresh ones. IFNgamma production from the frozen PBMCs was significantly higher than that from the fresh ones (P<0.01). In contrast, IL-6 level from the frozen sample was significantly lower than that from the fresh one (P<0.05). Those results indicate that cryopreservation can increase the sensitivity of porcine PBMCs stimulated by PMA for IFNgamma production but not for IL-6 production. There was no significant difference of IL-4 production between fresh and frozen cells either stimulated (P>0.05) or un-stimulated (P>0.05).