Sequential changes in flow rate of whole saliva are detailed in 13 patients. Samples were collected without exogneous stimulation during a course of fractionated radiotherapy involving major portions of the salivary glands. Flow rate decreased markedly during the initial 3 treatment days and gradually thereafter until a minimal flow rate was reached. Early in the treatment, variable degrees of recovery were seen on Mondays following a weekend (Friday-Sunday) without treatment. After a minimal flow rate was reached, no such recovery was observed. Radiation needed to produce minimal flow varied from 450 to 4,050 rad. Patients with higher initial flow rates required higher dosages to reach the minimum. No return of secretory function was noted after extended periods of time.