The use of empirical and mechanistic approaches are possible in the development of tests to screen for a substance's potential to affect interspecies interactions. The advantages and disadvantages of the two approaches are discussed. An experimental study is presented in which an empirical and a mechanistic screening test for effects on exploitative competition between bacterial species were established and perturbed with nalidixic acid. Comparison of test results indicates that the mechanistic test was faster, cheaper, more sensitive, and more quantitative. The empirical test attained similar sensitivity and quantification only if the dynamics of the competition event was continuously monitored; requiring even greater cost and time.