OBJECTIVE To assess chemoradiotherapy-induced salivary gland dysfunction using quantitative salivary gland scintigraphy (QSGS), and whether QSGS is capable of predicting the grade of persistent salivary dysfunction after chemoradiotherapy. METHODS From a time-activity curve using a stimulation test, the washout rate (WR) calculated was assessed. All glands (n = 155) were classified into four groups: a no-therapy group (n = 18), a chemotherapy alone group (n = 31), a radiotherapy alone group (n = 50), and a chemoradiotherapy group (n = 56). Subjective descriptions of xerostomia were recorded 1 year after the completion of the treatment period, and the 32 glands subjected to irradiation with or without chemotherapy were assessed. RESULTS The WR values were significantly lower in glands that received chemoradiotherapy than in glands treated with radiotherapy alone (mean: 0.75 x 10(-3), n = 40 vs. 0.22, n = 36, p < 0.015), but there was no significant difference in the WR values between the no-therapy group and the chemotherapy alone group. The mean values of WR were lower in the chemoradiotherapy glands than in the radiotherapy alone glands in each of cumulative dose ranges of 1-20, 21-30, and 31-60 Gy. With regard to recovery from xerostomia, the WR values at a cumulative dose range of 20 to 40 Gy were significantly lower in the not improved group (-0.418, n = 16) than in the improved group (0.245, n = 16) (p < 0.0001). CONCLUSIONS Chemotherapy per se has no or little adverse effect on salivary function, but combination chemotherapy can deteriorate radiation-induced injury of the salivary glands. QSGS appears useful in predicting the grade of persistent xerostomia following chemoradiotherapy.