The floor plate, a cell group that develops at the midline of the neural plate in response to inductive signals from the notochord, has been implicated in the control of dorsoventral neural pattern. The frog Pintallavis gene, encoding a member of the HNF-3/fork head transcription factor family, is expressed in the notochord and in midline neural plate cells that give rise to the floor plate. To examine whether Pintallavis might be involved in regulating the differentiation of the floor plate, we ectopically expressed Pintallavis by injection of synthetic mRNA into two-cell frog embryos. Injection of Pintallavis mRNA resulted in the ectopic expression of F-spondin, a gene encoding a floor plate-specific adhesion molecule, at the dorsal midline of the neural tube. The expression of Pintallavis in midline cells may therefore contribute to the establishment of the floor plate fate.