Diagnostic value of transient pattern electroretinogram (PERG), recorded by skin electrodes, was compared with Goldmann perimetry in cases of ocular hypertension and glaucoma. According to the assumption that the PERG mostly reflects activity of the retinal ganglion cells, and histological evidence that 30-50% atrophy of the retinal ganglion cells is necessary to cause defects in visual field, we wanted to assess if i) this method could be more sensitive in detecting early glaucomatous damage than routine Goldmann perimetry in eyes with normal or only borderline elevated intraocular pressure in the time of PERG recording (first group of patients), and ii) how the PERG amplitude corresponds to ganglion cell loss, expected in the eyes with already detectable initial glaucomatous visual field defects, according to Goldmann II/2 isopter, with normal or borderline elevated intraocular pressure in the time of PERG recording (second group). In the group with no visual field defects subnormal amplitude of the major positive component of the PERG, N1-P1, was detected in three of 30 eyes (10%), while in the group with initial visual field defects N1-P1 amplitude was subnormal in 6 of 11 eyes (54%). The amplitude of the major negative PERG component, P1-N2, was found normal in all eyes of the first group and subnormal in 5 eyes (45%) of the second group.