The salivary gland function of 47 patients treated by radical radiotherapy (CHART or conventionally fractionated treatment) for head and neck cancer has been studied before, during and for up to 12 weeks from the start of treatment. Pronounced falls in salivary flow and pH are seen once radiotherapy has commenced, particularly when both parotid glands are included in the treatment volume. The initial rate of reduction in flow reflects the rate of delivery of treatment. The parotid glands show the greatest sensitivity to radiotherapy compared with the other salivary glands and reduction in salivary flow is dependent on both dose and the proportion of the gland included in the treatment volume. These early changes in salivary gland function are as marked for patients receiving either CHART or conventionally fractionated treatment, so differing from the late changes which have been shown to be less evident after CHART.