Valproic acid (VPA) is an anti-convulsant drug known to cause spina bifida in humans. Administration of the vitamin, folic acid, has been shown to decrease the recurrence and possibly also the occurrence of neural tube defects, primarily spina bifida, in humans. Additionally, treatment with a derivative (folinic acid) of folic acid has been reported to decrease the frequency of VPA-induced exencephaly in mice treated with the drug in vivo. A protective effect by folinic acid has not been observed in vitro. The purpose of this investigation was to reexamine the ability of folinic acid to decrease the incidence of VPA-induced neural tube defects in vivo. We also examined the effect of increased intake of folic acid on zinc levels in various maternal and embryonic tissues. Folinic acid, whether administered by intraperitoneal injection or in osmotic mini-pumps, did not decrease the number of mouse fetuses with VPA-induced exencephaly. Dietary supplementation with 10-20 times the daily required intake of folic acid in rodents also failed to decrease the embryotoxicity of VPA. Such dietary supplementation had no effect on zinc levels in maternal liver, brain, or kidney, nor in embryonic tissues. These results indicate that folic acid is not able to reverse the embryotoxicity induced by the anticonvulsant, that there is no apparent effect of high dietary folate intake on maternal or embryonic zinc levels and suggest that folate is probably not involved in the mechanism of VPA-induced embryotoxicity.