Recent researches showed that basal cells in the olfactory epithelium were a stem cell population for renewal of olfactory receptor neurons. In order to find out whether vitamin A therapy is effective for regeneration of olfactory receptor cells, our examination was conducted to determine whether or not vitamin A treatment to the mouse increase labelling index of basal cells with 3H-thymidine at various time after experimentally induced olfactory receptor cell death. It was shown that there was an increase in 3H-thymidine uptake in the vitamin A injected animals in 1, 3, 5 days after olfacory epithelium destruction. However in 2, 7, 14, 21 days after intranasal treatment of 1% zinc sulfate, no difference was noted in 3H-thymidine uptake between the two groups that vitamin A has been injected or not. Therefore, our present study suggests that vitamin A might be useful in regeneration of olfactory neurons in the early days of trauma though little information is avaliable on the mechanism that may govern this phenomenon.