Previous investigations have indicated that striated-duct cells react to stimulation with an apocrine secretion, morphologically demonstrated by bleb-like projections of the apical cytoplasm. Since bleb formation as an ultrastructural feature also has been debated and sometimes interpreted as a fixation artifact, it was considered essential to extend the studies by exposing the submandibular gland to X rays to establish whether such treatment would have any influence on the formation of blebs. The material used in the present study consisted of rat submandibular glands exposed to X rays in the range of 200—1800 rad. The glands were examined by both SEM and TEM. The duct cells exposed to 200 rad appeared normal, with no sign of alteration in their ability to produce blebs, whereas duct cells exposed to 750 rad showed no sign of bleb formation. Some of the duct cells exposed to 1800 rad showed considerable morphological changes, consistent with oncotic transformation. The results support the conclusion that bleb formation is a normal morphological feature and not an artifact. This study also indicates that the functional activity of the cells is reduced after exposure to X rays.