In order to examine the influence of X-ray irradiation on the demilune cells of the sublingual gland due to the existence of secretory granules, 10 Gy of X-ray irradiation was applied to the sublingual gland of mice at 3 hours after isoproterenol (IPR) administration. To inspect the influence of irradiation at 3 days after the irradiation, tissue images and results of autoradiography performed at 30 and 120 minutes (min) after ³H-leucine administration of the IPR administration (IPR/10Gy) group were compared with those of the non-IPR administration (nonIPR/10Gy) group. In transmission electron microscope images, swelling and pyknosis were observed in the rough endoplasmic reticulum of the nonIPR/10Gy group. The number of reduced silver grains per unit cell area in nonIPR/10Gy at 30 and 120 min after ³H-leucine administration was less and greater than that in the other 3 groups (nonIPR/0Gy, IPR/0Gy, and IPR/10Gy), respectively, from light microscope autoradiography images. At 120 min after ³H-leucine administration, the ratio of the number of reduced silver grains localized in the secretory granules to the total number of reduced silver grains in the demilune cells of the nonIPR/10Gy group was lower than that of the other 3 groups as indicated by electron microscope autoradiography images. Based on these results, it was apparent that the effect of irradiation was less on the demilune cells that discharged secretory granules than those that did not discharge them.