Fumonisin B 1 (FB 1), a potent mycotoxin prevalent in corn, is a carcinogen and causative agent of various animal diseases. Species and sex variations to chronic FB 1 toxicity have been reported. Free sphingoid bases and cytokine levels are the two major biochemical alterations of FB 1 in vivo and may explain any sex differences in FB 1 toxicity. Male and female BALB/c mice (5/group) were injected subcutaneously with either saline vehicle or 2.25 mg/kg/day of FB 1 for 5 days. One day after the last injection females showed a greater increase in circulating alanine aminotransferase and greater number of apoptotic cells in liver after FB 1 treatment than males, indicating greater hepatotoxicity. Peripheral leukocytic counts, including neutrophils, were increased in females only after FB 1 treatment. The increased toxicity in females correlated with a greater increase of sphinganine and sphingosine levels in liver after FB 1 treatment compared to males. No sex differences in kidney sphinganine or sphingosine levels were observed after FB 1 treatment. Previously we have shown the induction of tumor necrosis factor α (TNFα) in FB 1-induced hepatotoxicity. While in males FB 1 treatment caused increased expression of TNFα, interleukin (IL)-12 p40, interferon γ (IFNγ), IL-1β, IL-6 and IL-10, females showed an increased expression of IL-6 only, and a downward modulation of IFNγ, indicating gender differences in cytokine pathways in liver activated by FB 1. The basal expression of TNFα, IL-12 p40, IL-1β and IFNγ in liver of females was higher compared to males. Gender differences in alterations of free sphingoid bases and cytokine modulation after FB 1 treatment suggest their possible involvement in sex-dependent differential hepatotoxicity in mice.