Neurogenesis in the olfactory epithelium begins in early embryos and proceeds throughout life. A comparison of neurogenic marker expression at different developmental stages and at different axes of the olfactory epithelium has not been reported in a coordinated way. In this study, we have in detail compared the temporal and spatial expression patterns of the precursor markers Hes5, Cash1, Ngn1, and the neuronal markers Gap43, HuC/D, Lhx2 in the developing olfactory placode and epithelium in chick embryos from HH10 to HH34. We show that Hes5 starts to be expressed in cells of the prospective olfactory placode at HH10, earlier then previously reported. During olfactory pit stages, the expression of Hes5, Cash1, Ngn1, Gap43, HuC/D, and Lhx2 varies throughout the anterior-posterior and superior-inferior axis of the olfactory epithelium. By HH34, expression of the precursor and neuronal markers show the first signs of apical-basal stratification of the epithelium. Developmental Dynamics 238:1617-1625, 2009. (c) 2009 Wiley-Liss, Inc.