The incidence of adverse effects on radiotherapy in head and neck cancer is quite common. Some irradiation doses affecting parotid gland have been investigated. 38 irradiated cases and 12 non-irradiated cases constituting the control group have been included in the study. Histologic examination, sialography, scintigraphy and sialometry have been performed in all cases. The impairment of parotid gland is evident in the early stage and is aggravated with time. Glandular function is not reduced significantly by irradiation doses of 2000-3000 r. A marked functional reduction has been noted with irradiation doses of 5000-6000 r., and is variable in each individual. The reduced glandular function was particularly reduced in the early postirradiation period. The subsequent functional improvement is related to the remainder of less affected parenchyma, reduced inflammatory process and rapid growth of goblet cells in the walls of the outlet system compensating mucus deficit.