A direct relationship between rose bengal concentration, light intensity, and the inhibition of linear growth ofAspergillus nigerwas demonstrated. Exposure of the fungus to a light intensity of 100 foot-candles for not more than 30 seconds daily was sufficient to cause inhibition of growth when the culture medium contained rose bengal in a concentration of 2 × 10−3 M. Rose bengal alone, in total darkness, apparently does not inhibit the growth ofA.niger. There appears to be a relation between the presence of rose bengal and light and the sporulation ofA.niger.