Tests were conducted to determine the dietary concentrations at which 14-d old bobwhite chicks could discriminate between food treated with two organophosphorus insecticides and untreated food. Results of subacute dietary LC50 tests using one feeder of treated food per cage were compared with those of tests in which birds were presented with two feeders, one treated, one not, or 10 feeders (5:5 or 9:1). The dietary concentration above which birds discriminated between treated and untreated feeders by consuming a greater proportion of untreated was defined as the discrimination threshold(DT). The DT occurred at sublethal dietary concentrations in all chlorpyrifos tests, but increased in the methyl parathion tests as the number of choices and the relative proportion of treated feeders increased. No relationship was found between mortality and the amount of active ingredient ingested per bird-day.