The study concerned the influence of a flash of light (a 2[degree] circular patch at 50 apparent foot candles lasting for 0.1 sec.) upon the audibility threshold for an accompanying tone (1,000 cycle tone lasting 0.165 sec.) when the interval between light and tone were varied. Each of 11 human subjects was given 720 stimulations to determine the audibility threshold under the various conditions. When the light and tone were simultaneous, or when the light preceded the tone by 0.5 sec. or 1 sec., there was a highly reliable increase, observed in all subjects, in the frequency with which near threshold tones were heard; the maximum effect occurred when the light preceded by 0.5 sec. When the light preceded the tone by 2 sec. there was no consistent facilitating effect. When the light followed the tone by 0.5 sec., it had no effect, for the average of the 11 subjects'' results, on the 1st 2 exptl. days, but a reliable facilitating effect on the 3d and 4th days. The maximum threshold shift for any condition was about 2 decibels. Possible mechanisms of the effect are discussed.