An investigation of the toxicity of fumonisin B1 (FB1), a toxic metabolite of Fusarium moniliforme, in broiler chicks was conducted. Purified FB1 (98.1% pure) was incorporated into the diets of broiler chicks at 0, 20, 40, and 80 mg/kg, and fed to chicks from 0 to 21 d of age. Dietary FB1, at concentrations of 80 mg/kg or less, did not adversely affect body weight, feed efficiency, or water consumption of broiler chicks. The relative weights of the liver, spleen, kidney, proventriculus, and bursa of Fabricius were also unaffected (P < 0.05) by any dietary concentration of FB1 compared with the control (0 mg/kg) group. Total liver lipids of chicks fed 40 or 80 mg FB1/kg were significantly lower than those of the chicks fed either 0 or 20 mg FB1/kg of feed. Liver sphinganine concentration and the sphinganine:sphingosine ratio were increased significantly in all treated groups. Chicks fed dietary FB1 at 80 mg/kg had significantly higher serum glutamate oxaloacetate aminotransaminase:aspartate aminotransferase ratios and levels of free sphinganine in the serum. The results of this investigation agree with the results previously described, in which FB1 was supplied to diets from the use of F. moniliforme-contaminated grain; therefore, the use of such material as the source of the mycotoxin in animal feeding studies is appropriate.