SUMMARYA total of 439 individuals with diabetes mellitus were examined for carriage of yeasts by the oral rinse and palatal swab techniques. Eighteen genetic or environment variables were assessed for their contribution to carriage of yeasts. The factor contributing to palatal and oral carriage of yeasts among individuals with insulin dependent diabetes mellitus (IDDM) was age (P < 0-01). The factor contributing to palatal carriage of yeasts among individuals with non-insulin dependent diabetes mellitus (NIDDM) was poor glyeaemic control (glycosuria P < 001); carriage in the oral cavity as a whole was influenced additionally by non-secretion of ABH blood group antigens (P < 0.05). Introduction of a denture altered the above risk factors. For individuals with IDDM, oral carriage was associated with the presence of retinopathy (P < 0 05); palatal carriage was influenced by poor glycaemic control (HbA,P < 001, plasma glucose levels P < 0-05) and age (P < 0 05). For those with NIDDM, palatal carriage was associated with continuous presence of the denture in the mouth (P < 0-01); oral carriage was associated with plasma glucose levels (P < 0 05).