A prospective study was undertaken of 22 patients with chronic hyperplastic candidosis and 50 age and sex matched individuals with no evidence of oral mucosal disease. Specifically the relationship between the inherited ability to secrete blood group antigens in saliva and chronic hyperplastic candidosis was investigated. The proportion of non-secretors of blood group antigens was significantly higher in patients with chronic hyperplastic candidosis (68%) compared to the control subjects (38%). The inability to secrete blood group antigens in saliva may therefore be a risk factor in the development of, or persistence of chronic hyperplastic candidosis.