The present methods for the assessment of the electroretinogram (ERG) make the exchange of data between laboratories difficult owing to differences in photostimulation and recording techniques. In this study it is suggested that in addition to present techniques the b wave to a wave relationship may be a useful index for evaluating the ERG. The ERG responses evoked by relatively bright flashes are recorded in the dark-adapted state. A plot of the b wave amplitude as a function of the a wave amplitude describes the functional integrity of the retina. A normally functioning retina should elicit an ERG response that fits the normal curve regardless of the apparatus used for ERG recording. The only constraint is the use of full-field illumination. This method is based on physiological considerations regarding the origin of the ERG components. Such a method will facilitate data exchange between centres and can also be used for clinical assessment of the retina.