The function of the parotid glands in patients treated by three different schedules of radiotherapy was studied 9 months or more after its conclusion. All had received radiotherapy for a malignancy confined to one side of the head and neck region and only the gland on the side of the lesion was in the treatment volume; the contralateral gland acted as an internal control. Saliva was selectively collected from the parotid glands and the stimulated flow rate and pH of the saliva determined. Flow rates were expressed in each case as a percentage of that of the contralateral ("untreated") gland. Twelve glands that had received conventionally fractionated radiotherapy to a dose of 60-66 Gy showed a mean percentage flow of 20% and a significant fall in the pH of the saliva produced. Six glands that had received CHART and eight conventionally fractionated radiotherapy to a dose of 35-40 Gy showed mean percentage flows of 57 and 65%, respectively, with only slight and non-significant falls in saliva pH. The results show that in the treatment of squamous cell carcinoma in the head and neck the use of CHART can lead to considerably less late change in the function of the parotid gland.