Groups of 5-6 pregnant F344/N rats were dosed (po) from d 8 to 12 of gestation with 30 or 60 mg purified fumonisin B1 (FB1)/kg body weight, or with a fat-soluble extract of Fusarium proliferatum/corn culture derived from an amount of corn culture that would provide approximately 60 mg FB1/kg. Control rats were dosed with water or corn oil. Food intake was monitored daily during dosing. Fetal bone development was examined after staining with alizarin red, whereas internal organ development was examined in hematoxylin and eosin-stained tissue sections. Although group differences in maternal body weight were not statistically significant, weight was 6% less in dams dosed with 60 mg FB1/kg compared with the control group (p < 0.12). Relative litter weight was significantly suppressed by 60 mg FB1/kg. Ossification of the sternebrae and vertebral bodies was significantly impaired by FB1 treatment. Litters from mothers treated with a fat-soluble extract of F proliferatum/corn culture did not have suppression of weight or impairment of bone development. Fumonisin B1 is fetotoxic to rats by suppressing growth and fetal bone development.