The loss of salivary gland function after a single dose of 15 Gy was correlated to loss of gland weight and degeneration of seromucous acini and serous tubules at 10 months postirradiation. The serous tubules were degranulated rather early, but regenerated after some months in an abnormal way as adenomatous structures. Striated ducts were mainly unaffected by irradiation. Arterioles showed slight to moderate narrowing of the lumina. There was an increased amount of plasma cells in the gland lobules at 10 months postirradiation. Histologic and morphometric criteria and changes in gland weight showed less pronounced radiation injury in glands irradiated during inhibition of the gland function by biperiden (Akineton) compared to glands irradiated during stimulation of the gland function by pilocarpine. This finding may offer a clinically important means to reduce salivary gland dysfunction after radiation treatment of tumors in the head and neck regions.