The roles of Pax6 were investigated in the murine eye and the olfactory epithelium by analysing gene expression and distribution of Pax6-/- cells in Pax6+/+ ' Pax6-/- chimeras. It was found that between embryonic days E10.5 and E16.5 Pax6 is autonomously required for cells to contribute fully not only to the corneal epithelium, where Pax6 is expressed at high levels, but also to the to the corneal stroma and endothelium, where the protein is detected at very low levels. Pax6-/- cells contributed only poorly to the neural retina, forming small clumps of cells that were normally restricted to the ganglion cell layer at E16.5. Pax6-/- cells in the retinal pigment epithelium could express Trp2, a component of the pigmentation pathway, at E14.5 and a small number went on to differentiate and produce pigment at E16.5. The segregation and near-exclusion of mutant cells from the nasal epithelium mirrored the behaviour of mutant cells in other developmental contexts, particularly the lens, suggesting that common primary defects may be responsible for diverse Pax6-related phenotypes.