Lethal dye-sensitized photooxidation reactions in the black imported fire ant,Solenopsis richteri(Forel), have been defined as a function of whole body concentrations of a series of xanthene dyes. Log probit analysis of mortality data has allowed calculation of LD50values of 1.1×10−3M for dietary levels and 2.3×10−7moles/ gm wet weight for whole body concentrations of rose bengal in ants illuminated with 3800 μW/cm2light for 4 h. Comparative LT50values were calculated for the xanthene dye series and related to whole body dye concentrations.