In this study we describe certain aspects of normal variability of oscillatory potentials, with particular reference to interaction between pupil size and stimulus intensity. The mean latencies of the earlier oscillatory potentials, O1 and O2, were significantly shorter when adopting the dilated pupil condition than when stimulating with a normal pupil. This occurred at various light intensities, although the difference was more significant at the highest intensity. O1 and O2 latencies became significantly longer as the stimulus intensity was progressively reduced. The latencies of the later components O3 and O4 were unaffected. The O1 and O2 amplitudes were not influenced by pupil size, but a significant reduction occurred with the progressive decrease in stimulus intensity. The later components O3 and O4 are greatly reduced in amplitude after pupil dilatation using higher stimulus intensities; the O4 potential may even disappear in 10% of the cases. These data provide further support for the existence of two distinct behavior patterns for earlier and later oscillatory potentials. Although light adaptation may affect oscillatory potentials, we suggest that in our experimental conditions, oscillatory potential changes may occur as a result of the activity of the neural modulating system, not only as a result of photoreceptor interaction.