Mycotoxins are secondary fungal metabolites that grow on a variety of feed and food. The clinical toxicological syndromes caused by ingestion of moderate to high amounts of mycotoxins are very diverse. Consumption of lesser amounts of fungal toxins may result in impaired immunity. Fumonisin B₁ (FB₁) belongs to the fumonisin toxins which are produced by Fusarium verticillioides, fungi that commonly contaminate corn. Recent surveys on fumonisins in food and feed throughout the world have raised concerns about the extent of FB₁ contamination of corn and implications for food safety as well as human and animal health. At high concentrations, FB₁ causes a variety of species-specific toxicological effects in domestic and laboratory animals. Disruption of sphingolipid metabolism is an important aspect of the toxicity of FB₁ and it has implications on the immune response. The synthesis of both inflammatory and regulatory cytokines is affected by FB₁ treatment. Among inflammatory cytokines, a particular attention has been brought to TNF-α. FB₁ increases the synthesis of this cytokine which plays an important role in the toxicity of the mycotoxin. The expression of other inflammatory cytokines such as IL-12p40, IL-1β, IL-8 and IL-18 is also increased during FB₁ intoxication. The induction of inflammatory cytokines is correlated with an increase of the synthesis of Th1 type cytokines (such as IFN-γ) and a concomitant decrease of the synthesis of Th2 type cytokines (such as IL-4). The alteration of the Th1/Th2 cytokine balance is associated with a decrease of the antibody response with an implication for the immune response to vaccination.