Bioinformatics programs have helped tremendously in identifying the targets of microRNAs, which are small noncoding RNAs that regulate gene expression posttranscriptionally. However, the partial complementarity between miRNAs and their targets hinders the accuracy of target prediction, necessitating the use of experimental validation procedures. Here, we describe a gene reporter assay typically used in our lab to validate putative miRNA-mRNA interactions in Drosophila S2 cells.