Repopulation of tissues with cells at damaged sites is an important feature in the recovery of radiation-induced tissue injury. To obtain insight into the regenerative process in salivary gland tissue, proliferative activity was measured as a function of time in the different epithelial cell compartments of rat parotid and submandibular glands after local X irradiation with a single dose of 15 Gy. Bromodeoxyuridine-labeling indices were determined before and 10 h and 1, 3, 6, 10, 15, 20 and 30 days after irradiation. In both glands, X irradiation caused cell death and cell cycle delay manifested during the first day. Three days after irradiation, cell proliferation started in the intercalated duct. Six days after irradiation, proliferation was also observed in acinar and granular convoluted tubule cells. The striated ducts showed proliferative activity starting at day 6 (parotid) and day 10 (submandibular), respectively. The results of this study suggest that after 15 Gy of X rays repopulation takes place in all cell compartments. From the present study it cannot deduce if these cells are originating solely from progenitor cells residing in the intercalated duct or if cells of the other compartments are also stimulated. Proliferative activity was found to be higher in the intercalated duct compartment of the parotid gland than of the submandibular gland, which may be related to the suggested greater radiosensitivity and thus a greater demand for cell replenishment in the parotid gland.