Improper disposal of Municipal solid wastes (MSWs) is one of the major sources of environmental pollution in India. Leachates from these wastes contaminate our water sources. This study was carried out to determine the toxic effects of leachates from MSW in transgenic Drosophila melanogaster (hsp70-lacZ). Organisms were examined for Hsp70 expression, oxidative stress enzymes, proteotoxicity, tissue damage and effect on emergence and reproduction. Chemical analysis alone does not give insight into the biological effects of complex chemical mixtures (leachates).Bioassays are an important tool in this regards. The study emphasizes on the use of efficient biomarkers and sensitive bioassays, along with chemical analysis as a toxicological approach against complex mixtures. This approach would help in evaluating the toxic potential of chemical mixtures in our environment. The study highlights the advantage of Drosophila as an alternate animal model, advocating Hsp70 as the ?rst-tier indicator of toxicity. The study should help researchers and toxicologists in understanding the approach of using multiple biomarkers/bioassays for toxicological evaluation of complex chemical mixtures.