The floor plate (FP) is a transient structure of the embryonic central nervous system (CNS) which plays a key role in development driving cell differentiation and patterning in the ventral neural tube. The fact that antisera raised against subcommissural organ (SCO) secretion immunostain FP cells and react with high-molecular-mass proteins in FP extracts, prompted us to investigate the expression of a SCO-related polypeptide in FP cells. RNA from bovine FP was analyzed by means of reverse transcriptase polymerase chain reaction (RT-PCR), using primers derived from the 3' end of SCO-spondin which revealed products of 233, 237, 519 and 783 bp. Sequence analysis of the 233 bp PCR fragment confirmed the identity between this FP product and SCO-spondin. FP-translation of the SCO-spondin encoded polypeptide(s) was demonstrated by Western blot analysis and immunocytochemistry, using antisera raised against (i) the glycoproteins secreted by the bovine SCO, and (ii) a peptide derived from the open reading frame of the major SCO secretory protein, SCO-spondin, respectively. Additional evidence pointing to active transcription and translation of a SCO-spondin related gene was obtained in long term FP organ cultures. On the basis of partial sequence homologies of SCO-spondin with protein domains implicated in cell-cell contacts, cell-matrix interactions and neurite outgrowth it is possible to suggest that the SCO-spondin secreted by the FP is involved in CNS development.