The pattern electroretinogram (PERG) reflects the activity of the retinal ganglion cells. To assess its value to detect early glaucoma damage, we recorded the PERG in 44 normal eyes, in 52 eyes with early stages of glaucoma, and in 34 eyes with elevated intraocular pressure but normal visual fields (ocular hypertension, OHT). All eyes had a decimal acuity of greater than or equal to 0.8. We used checkerboard patterns for the stimulation with check sizes of 0.8 degrees and 15 degrees, a contrast of 98% and a reversal rate of 16/s. Compared to the controls, in eyes with early glaucoma PERG amplitude was reduced to 50% using 0.8 degrees (p less than or equal to 0.0001) and to 74% using a check size of 15 degrees (p less than or equal to 0.001). However, due to the high interindividual variability, confidence limits overlapped to a large extent. Based on the preferential reduction at 0.8 degrees vs 15 degrees, a sensitivity of 74% and a specificity of 92% were achieved using a two-dimensional logistic regression; 50% of the OHT eyes were thus classified as pathological. These results suggest that the PERG can detect retinal ganglion cell damage before measurable changes in the visual field occur if responses to two check sizes are evaluated.