Lens and cornea autofluorescence has been shown to be increased in patients with insulin-dependent diabetes mellitus and to be positively correlated to glycaemic control and duration of diabetes. We have studied lens and cornea autofluorescence at the clinical onset of non-insulin-dependent diabetes mellitus (NIDDM), in comparison with age-matched subjects with normal glucose tolerance. Fourteen subjects with NIDDM diagnosed less than 6 months prior to the examination were characterised by ocular fluorometry, glycosylated hemoglobin A1c, plasma lipid status, arterial blood pressure, and an oral glucose tolerance test (OGTT). Eleven age- and gender-matched healthy subjects without a family history of diabetes and with a normal glucose tolerance underwent the same examinations. In 11 of the 14 diabetic patients lens autofluorescence was increased to levels higher than the age-related mean + 2SD of healthy subjects. For the entire study population, control and diabetic subjects, lens fluorescence was positively correlated with HbA1c (p < 0.0001, r = 0.73), fasting plasma glucose (p = 0.002, r = 0.60) and the plasma glucose level 2 h after an OGTT (p = 0.004, r = 0.55). Cornea autofluorescence was also significantly increased in the group of newly diagnosed NIDDM patients, but only 9 patients had values above the mean + 2SD of the healthy subjects. NIDDM could be detected by ocular fluorometry with a sensitivity of 79% and a specificity of 100%. We conclude that lens and cornea autofluorescence is abnormally increased in the majority of patients with newly diagnosed NIDDM. The sensitivity and specificity of the method indicate that lens fluorometry may potentially be useful for screening for undiagnosed NIDDM in the general population. Additionally, we propose that the method may be a clinically useful indicator of cumulative glycaemia and risk of development of secondary complications in patients with diabetes.