Fetuses of pregnant CD-1 mice, exposed to 0.1% nicotine sulfate at a dose of 1.67 mg/kg body weight from the 6th through the 15th gestational days were compared with control fetuses to assess the effects of nicotine on tongue development. Mothers were sacrificed on the 18th gestational day. The heads of a total of 130 nicotine-treated and 348 control fetuses were embedded in paraffin and sectioned in the frontal plane. 9.6% of the nicotine-treated fetuses had palatal clefts and their tongue development was much retarded compared to the controls. The tongues of the clefted fetuses were misshaped, reduced in size, had no filiform or fungiform papillae, and their myotubes were just in the process of formation. The circumvallate papilla of these fetuses were present but neither taste buds nor glands of von Ebner had as yet developed. Tongue development of nicotine-treated, non-clefted fetuses were closer to those of the controls. The anlagen of their filiform and fungiform papillae were developing, their myotubes were longer and better arranged, their circumvallate papilla was present but without taste buds, and their glands of von Ebner were not developed. It is suggested that nicotine interferes with both palatal and mesenchymal components of tongue development.