Abstract The stimulus characteristics which constitute edge information for the visual system were studied by investigating the manner in which edge luminance is related to reduction in apparent brightness in metacontrast masking. Both targets and masks were briefly-flashed, nonoverlapping, rectangular apertures in which the luminance was modulated spatially in the horizontal dimension. The edge gradient was either gradual, a step function, or a step function with an additional spatial transient. The results showed that reduction in apparent brightness of the target is strongly influenced by the edge luminance of both the target and the mask. The data are discussed in terms of possible underlying mechanisms and with respect to other apparent brightness phenomena.