A prototype automated flicker perimeter was used to investigate flicker luminance thresholds in glaucoma patients (n = 11), ocular hypertensives (high risk n = 10, low and intermediate risk n = 21) and normal controls (n = 10). Differential light sensitivity was measured for one eye of each subject using a flickering stimulus at frequencies of 5, 10, 15, 20 and 25 Hz at ten test locations of 1 degree in the arcuate and nasal regions of the central 50 degrees of the visual field using a 4-2 dB staircase. The glaucoma patients had significantly reduced sensitivities for all frequencies (p < 0.001) with minimum sensitivity at 15 Hz. The 'high risk' ocular hypertensives had significantly reduced sensitivities at 10 and 15 Hz (p < 0.02). At present the ocular hypertensive patients in this study show no abnormalities demonstrable by conventional automated static perimetry. These findings may represent the earliest of perimetric deficits in patients with glaucomatous optic neuropathy.