The ultrastructural phenomena of obstructive palatal sialadenitis were studied in 7 denture wearers versus 3 non-denture wearers as control. Apart from mucositis severe stagnation of salivary flow in the excretory ducts was observed in patients with dentures with short periods of service. In contrast to the control group there were mucous droplets after exocytosis of the acinus cells that remained intact even in the lumina of the distal excretory ducts. Desquamation of the duct and acinus cells results in a change in the organic components of the secretory mucus. The periductal infiltrate consisted mainly of plasma cells and lymphocytes, whereas neutrophils or macrophages were not observed. Ultrastructurally there was no evidence of an ascending microbial infection of the ducts. Probably, infections do not play an important role in the pathogenesis of obstructive palatal sialadenitis.