Technical Abstract: Fumonisin (FB) and moniliformin (MN) are Fusarium mycotoxins that co-occur in corn and foods. Their effect on human health is unclear, but both have been implicated as a contributing factor to one or more diseases. FB is hepato- and nephrotoxic in various species and causes liver and kidney cancer in rodents. The heart is not considered a target organ in rodents, but FB does affect cardiac function in swine in vivo and in frog heart atria in vitro. The heart, kidney, and liver are target organs of MN in poultry and rats. Additive toxicity has been found in poultry co-exposed to FB and MN. To study the effect of co-exposure in a mammalian species, male rats (2 replicate experiments of n=3/group per replicate) were fed diets spiked with FB-producing (fumonisin B1 + B2 + B3) Fusarium verticillioides and MN-producing F. fujikuroi culture materials for two weeks ad libitum. Mycotoxin concentrations in the diets were: 0 ppm FB/0 ppm MN (control group), 400 ppm FB/0 ppm MN, 400 ppm FB/200 ppm MN, or 400 ppm FB/500 ppm MN. The replicate experiments yielded similar results. All FB-fed groups exhibited decreased body weight, decreased relative (% body weight) liver and kidney weights, and increased tissue sphinganine concentrations indicative of ceramide synthase inhibition. Apoptosis and other microscopic liver and kidney lesions were also consistent with FB toxicity and, like the other effects, were not modified by MN. Relative heart weight (% body weight) of the 400 ppm FB/500 ppm MN group was slightly increased, however, gross or microscopic heart lesions were not found in any group. In summary, MN did not significantly modify the subchronic toxicity to rats of FB-containing diets. Further investigations are needed to study the effects of chronic co-exposure to MN and FB.Fumonisin (FB) and moniliformin (MN) are Fusarium mycotoxins that co-occur in corn and foods. Their effect on human health is unclear, but both have been implicated as a contributing factor to one or more diseases. FB is hepato- and nephrotoxic in various species and causes liver and kidney cancer in rodents. The heart is not considered a target organ in rodents, but FB does affect cardiac function in swine in vivo and in frog heart atria in vitro. The heart, kidney, and liver are target organs of MN in poultry and rats. Additive toxicity has been found in poultry co-exposed to FB and MN. To study the effect of co-exposure in a mammalian species, male rats (2 replicate experiments of n=3/group per replicate) were fed diets spiked with FB-producing (fumonisin B1 + B2 + B3) Fusarium verticillioides and MN-producing F. fujikuroi culture materials for two weeks ad libitum. Mycotoxin concentrations in the diets were: 0 ppm FB/0 ppm MN (control group), 400 ppm FB/0 ppm MN, 400 ppm FB/200 ppm MN, or 400 ppm FB/500 ppm MN. The replicate experiments yielded similar results. All FB-fed groups exhibited decreased body weight, decreased relative (% body weight) liver and kidney weights, and increased tissue sphinganine concentrations indicative of ceramide synthase inhibition. Apoptosis and other microscopic liver and kidney lesions were also consistent with FB toxicity and, like the other effects, were not modified by MN. Relative heart weight (% body weight) of the 400 ppm FB/500 ppm MN group was slightly increased, however, gross or microscopic heart lesions were not found in any group. In summary, MN did not significantly modify the subchronic toxicity to rats of FB-containing diets. Further investigations are needed to study the effects of chronic co-exposure to MN and FB.