Oct-6 is a POU transcription factor that is thought to play a role in the differentiation of cells of neuroectodermal origin. To investigate whether the Oct-6 protein could play a role in the establishment of neuroectoderm in vivo we studied the expression of the Oct-6 protein during early mouse development. Expression is first observed in the primitive ectoderm of the egg cylinder stage embryo. In gastrulating embryos, Oct-6 protein is found in the extra-embryonic ectoderm of the chorion and the anterior ectoderm of the embryo proper. As development proceeds, Oct-6 expression becomes more restricted to the anterior medial part of the embryo until Oct-6 positive cells are observed only in the neural groove of the headfold stage embryo. In the late headfold stage embryo, Oct-6 expression is detected in the neuroepithelium of the entire brain and later is restricted to a more ventral and anterior position. As the anterior neuropore closes, Oct-6 protein is detected in a segment-like pattern in the mid-and forebrain. Thus, the expression pattern of the Oct-6 gene agrees with a role for the Oct-6 protein in the establishment and regional specification of the neuroectoderm in vivo. The two waves of widespread induction of the Oct-6 gene, one in the primitive ectoderm and another in the primitive brain, both followed by a progressive restriction in the expression patterns suggest a mechanism for the regulation of the gene.