Earlier studies have suggested that the absolute threshold to light can be raised by certain irrelevant stimuli, such as a tone, that had previously been presented many times in the presenec of adapting lights. An attempt was made to confirm this finding. 2 groups took part, each consisting of 6 Ss. The 1st group received a combination of a tone and a moderately bright light, the 2nd a tone and a weak red light. Later, the threshold was measured in the presence of the tone alone. Of the 2 groups, the 1st gave consistently higher thresholds. The effect is not attributable to adaptation. It is concluded that at least the possibility of the conditioning of the absolute threshold exists. (PsycINFO Database Record (c) 2006 APA, all rights reserved)