Reproduction in individual animals of sexual species depends largely upon their ability to detect and distinguish specific signal(s) among those produced by various potential sexual partners. In Drosophila melanogaster males, there is a natural polymorphism for discrimination of female and male principal pheromones that segregates with chromosome 3. We have mapped two loci on chromosome 3 that change sex-pheromone discrimination in males. We successively exploited meiotic recombination, deficiencies and enhancer-trap strains; excision of the transposon in two selected enhancer-trap strains clearly reverted the discrimination phenotype. These results indicate that pheromonal discrimination is a character that can be genetically manipulated, and provide further insights into the evolution of the specific mate recognition system.