We have measured the perceptive field, the psychophysical correlate of the physiologically determined receptive field, in man and monkey. Measurements were made using the Hermann grid illusion and the Westheimer paradigm. The following results were found: First, in both man and monkey, the size of perceptive fields and field centers increases from the fovea to the periphery. As with receptive fields, this increase is first rapid and then more gradual; and it is more pronounced on the temporal than on the nasal side of the retina. Second, monkey and human perceptive field centers are approximately the same size. But total perceptive fields (i.e., centers plus surrounds) tend to be smaller in monkeys. Third, in monkey, psychophysically measured perceptive field centers are about the same size as neurophysiologically measured receptive field centers. And as these, they are larger, by a factor 1.3-2, than histologically measured dendritic fields. These findings strongly indicate that in monkey all three measurements refer to the same underlying retinal mechanism. The same relationship is assumed to hold in man.