Computerized IR videopupilography, using an open-loop photic stimulator, was used to compare the reflexes of borderline diabetics with overt non-insulin-dependent diabetics and with age- and sex-matched non-diabetic healthy controls. The patients were all male, aged 41-59 years. Overt non-insulin-dependent diabetics in their 40s had a smaller pupillary area and pupillary diameter prior to photic stimulus compared with borderline diabetics and healthy controls. Overt non-insulin-dependent diabetics in their 50s had a lower pupillary area and pupillary diameter prior to photic stimulus, maximum velocity and acceleration of constriction and maximum velocity of dilation than did borderline diabetics or controls. The only abnormality observed among borderline diabetics compared to controls was a smaller amplitude of constriction in response to light in patients in their 50s. Amplitude of constriction in response to light and velocity of constriction measurements of borderline diabetics, however, were considerably more frequently abnormal than were those of controls. The frequency of abnormal pupillary diameter prior to photic stimulus, maximum velocity of dilation and acceleration of constriction was higher in overt non-insulin-dependent diabetics than in borderline diabetics. The results indicate that borderline diabetics have autonomic neuropathy before the disease becomes overt. The importance of the pupillary light reflex examination is discussed.