In the treatment of head and neck cancer by radiotherapy the major salivary glands are often inevitably included in the treatment volume. The impairment of salivary gland function that can result is an important cause of late morbidity following treatment. Clinical experience has suggested that impaired salivary gland function after radiotherapy is less following treatment using the CHART regime as compared with conventionally fractionated treatment. The salivary gland function of 73 patients treated by radiotherapy (CHART or conventionally fractionated treatment) for head and neck tumours has been studied. 26 were tested nine months to nine years after treatment and 47 were studied serially before, during and for up to 2 years after treatment. In 41 patients serum amylase was monitored before and during radiotherapy. Pronounced falls in salivary flow and pH are seen once radiotherapy has commenced when significant amounts of salivary tissue are included in the treatment volume. Marked rises in the serum amylase accompany these very early changes. The parotid glands show the greatest sensitivity to radiotherapy compared to the other salivary glands. The early changes are as marked for patients receiving either CHART or conventionally fractionated treatment but a greater recovery of function after CHART results in the improved function seen in patients nine months or more following treatment with CHART. The reduction in the late impairment of salivary gland function following radiotherapy with CHART is the result of the low dose per fraction employed combined with the reduced total dose. Patient comfort is greater and quality of life improved. Salivary gland function has proved measurable and is a valuable system for the study of human radiobiology. The evidence from this study gives support for the concept of reduced late change resulting from a reduction in dose per fraction, an area of importance to the development of improved radiotherapy treatment schedules.