The time interval between the incorporation of [3H]thymidine and the appearance of olfactory marker protein (OMP) in autoradiographically labeled neurons which have differentiated from stem cells, has been determined by autoradiographic and immunohistochemical techniques. The first [3H]thymidine-labeled, OMP-containing elements have been observed 7 days after administration of the radioactive thymidine. This result allows some speculation on the potential function of the olfactory marker protein.