Radiation damage to rat parotid acinar cells was evaluated by electron microscopy using exposures of 400, 800, 1600, and 6400 R. Evidence of intracellular damage was observed at all exposures by the presence of focal cytoplasmic lesions involving all of the organelles. The extent of the damage varied with dose, 400 R resulted in very mild injury while 6400 R caused extensive necrosis (1-4 days after irradiation) with signs of recovery in evidence by Day 6. In addition, at the lower doses, 400 and 800 R, the Golgi complex was found to be hypertrophied although at the higher doses, 1600 and 6400 R, this did not occur. Therefore, it was determined that x-irradiation results in histopathologic changes to the parotid gland at a relatively low dose and the extent of the damage varies directly with dose.