Radiation-induced damage to salivary glands has been recognized for over 80 years. However, the mechanisms responsible for the destruction of gland parenchyma are still not known. The purpose of this study was to describe alterations in salivary function in the rat within the first 24 h after irradiation. Saliva was collected from the parotid and submandibular glands during radiation treatment and at four times (0.5, 1, 4, and 24 h) after 15 Gy X irradiation delivered to the head and neck. Total body weight, submandibular gland weight, and food and water intake were monitored and the total protein, sodium, and potassium content of the salivas was analyzed. The effects of radiation on salivary glands of the rat could be demonstrated by 24 h. Parotid salivary flow was reduced and the sodium concentration was significantly less than that in control animals. Submandibular gland weights declined markedly by 24 h. These effects appear to be influenced significantly by the animals' limited intake of food and water during this period, as well as the anesthesia administered.