The autofluorescence of the crystalline lens has been measured by an ocular fluorophotometer in two comparable groups of patients with insulin-dependent diabetes mellitus. One group has had a high level of HbA1c since the onset of diabetes (mean 10.1 per cent) and the other group a very low level (mean 6.5 per cent). The group with low HbA1c during the disease period showed a significantly lower lens fluorescence than the group with high HbA1c.