Experiments in progress include: 1. Study of cell population dynamics in rat taste buds. Autoradiographic studies using 3H-thymidine labeling of taste bud cell nuclei are being done to estimate the life of dark and light cells in vallate and foliate papillae. Our data so far indicate the turnover time of the dark cells is 6-7 days. The data suggest also that there may be more than one population among the dark cells. The life of light cells is longer. 2. Immunohistological and immunocytochemical localization of marker protein in olfactory receptor cells of adult and developing mice and rats. The peroxidase-antiperoxidase conjugated antibody technique developed by Sternberger will be used. The technique will also be applied to specimens of olfactory tissue grown in organ culture.