One hundred and nine patients with diabetes mellitus and 100 age-, sex- and denture-status-matched, non-diabetic individuals were investigated prospectively. Comparison was made of oral candidal carriage, clinical infection and inherited ability to secrete blood group antigens in saliva. Diabetic patients had a significantly higher prevalence of oral candidal carriage and infection (P less than 0.001) than non-diabetic individuals, but the candidal load between the 2 groups, was not significant. A comparable proportion of insulin-dependent, non-insulin dependent and control groups were secretors of blood group antigens, and there was no difference in the oral candidal carriage and infection rates between secretors and non-secretors.