Chronic clinical irritation of the palatal mucosa by dentures involves a series of histological changes in epithelial and connective tissues, inflammatory cells and the vasculature. No single change is pathognomic of this inflammatory process. The rupture of basement membrane associated with the development of denture stomatitis often marks an important stage. This study investigated modifications in basement membrane organisation, especially the distribution of type IV collagen and a specific laminin chain (alpha1), during denture stomatitis. Biopsies of palatal mucosa were obtained from 12 patients (8 with denture stomatitis and 4 with clinically healthy mucosa) who had worn removable dentures for more than 3 years. Immunohistochemical studies performed with specific antibodies to type IV collagen and a laminin (alpha1) revealed strong expression in the basement membrane of healthy palatal mucosa. In denture stomatitis, some discontinuities or disruptions in basement membrane were observed at the interface between connective tissue and epithelial cells. These findings suggest a relationship between the expression of laminin (alpha1) and type IV collagen and the development of denture stomatitis, a disorder involving modification of soft tissues in which initial inflammation of the palatal mucosa results from stress under the denture. These changes in basement membrane can be detected by histological studies.