Clinical evaluation of the function of the human retina by subjective, psychophysical tests can be complemented by objective, electrophysiological methods such as electroretinography. The electroretinogram (ERG) is a transient action potential generated by the vertebrate retina in response to light. Using standardized stimulation, after assessing the normal range of the ERG the investigator can establish early diagnosis, improve prognostic statements and document the course of retinal diseases. A method to selectively stimulate the rod- and cone-system, developed by Gouras and co-workers, has proved to allow further differentiation of heredodegenerative diseases of the retina. The ERG monitors objectively the function of the retina in infants uncapable of cooperating in psychophysical tests and in patients suffering from opacities of the optic media. ERG results should be evaluated synoptically with psychophysical data, ophthalmoscopy, fluoresceinangiography and possibly with EOG and VER recordings. Under experimental conditions the ERG serves to monitor the sensitivity of the retina in vivo as well as in vitro in physiological, pharmacological and toxicological studies.