In this paper, experiments are described in which brightness constancy was studied in a Ganzfeld environment. Luminance variation by means of neutral density filters was applied to stimuli consisting of a Ganzfeld with superimposed disks. To this end, a special-purpose apparatus was constructed. Sequential dichoptical brightness matches with a reference stimulus were carried out for the disks as well as the homogeneous surround. The results of these measurements indicate that (1) besides a clear tendency toward brightness constancy, small but systematic effects of the average luminance level are present and (2) the brightness of the Ganzfeld is hardly affected by the presence of the disks. Finally, it is shown that the experimental results can be modeled adequately in terms of a concept that involves an accumulation of contrast information.