Fumonisin B1 (FB1), a secondary compound produced by toxigenic strains of Fusarium verticilloides and Fusarium proliferatum, is an important contaminant of cereals, especially maize (Pietri and Piva, 2000). Fumonisins, produced by Fusarium moniliforme, represent one of the five most important mycotoxin groups causing human disease. Although the toxic effect of mycotoxins in humans is very difficult to prove, based upon the toxicological results obtained so far, fumonisins are regarded as potential carcinogens. Farm animals are also susceptible to fumonisin, which causes equine leucoencephalomalacia. In poultry, chickens and turkeys can be considered relatively resistant, however, in young birds, a high dose of FB1 has been reported to cause growth retardation and liver damage. Ruminants are relatively resistant to fumonisin, but in young animals the toxin may cause reduced weight gain and hepatopathy (Zomborszky-Kovacs et al., 2002). It is well known that pigs are very susceptible to fumonisin and depending on its concentration, route of uptake and the duration of exposure, FB1 can cause rather diverse pathological lesions such as pulmonary edema, cardiovascular lesions, pancreatic necrosis (Harrison et al., 1990) and hepatic intoxication (Bucci et al., 1998; Gumprecht et al., 2001; He et al., 2001; Theumer et al., 2002). Unfortunately, until now, the effects of fumonisin on the cellular immune response of the pig and of its defence mechanisms are only partially understood. The aim of this study was to evaluate the behaviour and the susceptibility of T lymphocyte (CD4, CD8) and monocyte (CD14) subpopulations in piglets fed daily with a diet containing 30 ppm of Fumonisin B1 supplemented with 1% granulated activated carbon, as compared to piglets fed daily with a supplementation of only 1% granulated activated carbon, as detoxificant (control group) (Minervini, 2000).