Technical Abstract: Fumonisins (FB) are mycotoxins in maize and inhibitors of ceramide synthase (CS). In liver and kidney inhibition of CS results in a marked increase in the ceramide precursor sphinganine (Sa). This study was conducted to investigate the differential changes in Sa, sphingosine (So), Sa-1-phosphate (Sa-1-P) and So-1-phosphate (So-1-P) in kidney, liver, serum and heart of male Sprague-Dawley rats fed diets containing FB. The tissues were microscopically examined for the presence and severity of lesions. There was a time- and dose-dependent increase in Sa in both liver and kidney that was closely correlated with the tissue concentration of FB1 and histopathologic findings. However, the Sa and So were quickly metabolized to Sa-1-P and So-1-P in kidney. The concentration of FB1 in liver and kidney that first elicited an increase in Sa was similar in both tissues, however, over time, the kidney accumulated significantly more FB1 and total Sa (Sa plus Sa-1-P). Thus, the relative sensitivity of male Sprague-Dawley rat kidney and liver is most likely a consequence of differences in the mechanisms responsible for both FB1 uptake/clearance and Sa metabolism.