Fluorescence polarization assays in 384-well microtiter plates have been demonstrated, The performance is suitable for high throughput drug screening applications with respect to speed of analysis, displaceable signal, precision, and sensitivity to various reagents. Rank order of potency was maintained relative to [I-125]-ligand filtration assays, and the effects of the highly colored compounds, tartrazine and Chicago Sky Blue, were insignificant on the polarization signal up to a concentration of 1 mu M. These attributes suggest that accurate assessment of drug binding can be obtained.