The role of the central and peripheral stimulus fields on monocular and binocular amplitude and binocular summation of the pattern reversal visual evoked response were investigated. When the central stimulus field size was smaller than 2.4 degrees, there was no significant difference between the amplitude of the monocular and the binocular responses, but when it was equal to or larger than 3.2 degrees x 3.2 degrees, the binocular amplitude was significantly larger than the monocular. The value of binocular summation was highest at the central stimulus field of 4.0 degrees x 4.0 degrees; at larger sizes, there were no significant changes in the value. Use of a central stimulus field size larger than 3.2 degrees x 3.2 degrees was therefore considered a prerequisite for the effective assessment of visual function, especially binocular function, by means of the pattern reversal visual evoked response. With regard to the role of peripheral stimulus field on pattern reversal response, both the monocular and binocular responses, but particularly the latter, were found to be sensitive to a scotoma produced by covering the center of a full-field stimulus. The value of the binocular summation showed a significant reduction with a small central scotoma. We concluded that the pattern reversal visual evoked response is very sensitive to a central scotoma and that binocular function is mediated mainly through the central stimulus field.