Oral candidosis is common in patients with diabetes mellitus, as yeasts, particularly Candida albicans, have the propensity to colonise, form biofilms and release hydrolytic enzymes which cause inflammation. This study aimed to investigate these characteristics in isolates from three groups of patients with type 1 diabetes: individuals with better controlled diabetes (BCD; >or=6 <8%), individuals with poorly controlled diabetes (PCD; >or=8%) and non-diabetics (ND; HbA(1c) <5.9%). The biomass (Bm), phospholipase (P(z)), haemolysin (H(z)) and proteinase (Pr(z)) were assessed using a microtitre biofilm assay and agar-based hydrolytic enzyme assays. Biofilm formation was significantly increased in the PCD group compared to ND and BCD groups (P < 0.05). No significant differences in P(z) levels were observed between groups, whereas both H(z) and Pr(z) were significantly greater in the diabetes groups than in the healthy control group (P < 0.05). Statistically significant correlations were found to exist between the HbA(1c) levels of the patients and the Bm (R = 0.384; P = 0.033), haemolysin activity (R = -0.455; P = 0.010) and proteinase activity (R = -0.531; P = 0.002). There was no apparent correlation between the Bm and P(z) activity (R = -0.305; P = 0.053) or H(z) activity (R = -0.100; P = 0.296). However, a negative correlation was found between Bm and Pr(z) values (R = -0.343; P = 0.030). These data suggest that biofilm formation is likely to play a role in the pathogenicity of oral candidosis, and in patients with diabetes, this may be due to the ability of C. albicans to adapt to the altered physiological environment. The production of hydrolytic enzymes is independently associated with this growth modality.