Currently available primary screens for the selection of candidate antileishmanial compounds are not ideal. These techniques are time-consuming, laborious, and difficult to scale and require macrophages, which limit their use for high-throughput screening. We have developed Leishmania donovani field isolates that constitutively express the firefly luciferase reporter gene (luc) as a part of an episomal vector. An excellent correlation between parasite number and luciferase activity was observed. luc expression was stable, even in the absence of drug selection, for 4 weeks. The transfectants were infective to macrophages, and intracellular amastigotes exhibited luciferase activity. The suitability of these recombinant field isolates for in vitro screening of antileishmanial drugs was established. The luciferase-expressing sodium stibogluconate-resistant cell lines offer a model for the screening of compounds for resistance. The system is in routine use at the Central Drug Research Institute, Lucknow, India, for high-throughput screening of newly synthesized compounds.