Drosophila melanogaster flies use both olfactory and taste systems to detect sex pheromones and select the most suitable mate for reproduction. In nature, flies often face multiple potential partners and should have an acute sensory ability to discriminate between different pheromonal bouquets. We investigated both the pheromones and the chemosensory neurons influencing Drosophila mate choice. We measured various courtship traits in single tester males simultaneously presented with two target male and/or female flies carrying different pheromonal bouquets (pairs of control flies of the same or different sex, same-sex target pairs of pheromonal variant strains). The courtship traits reflected the perception of either olfactory cues perceived before or gustatory cues perceived after the first physical taste contact. Our results suggest that male mate choice exists in D. melanogaster and that male discrimination between potential mates could be a two-step process involving chemical cues perceived before and after the first gustatory contact. In addition, when a male was simultaneously presented with two potential sexual partners, the olfactory and gustatory cues he used depended on the pheromonal patterns of both flies, but his response could also depend on additional effects resulting from the simultaneous perception of the two flies, leading to a nonlinear choice of a sexual partner. Moreover, some tester males with genetically altered gustatory receptor neurons strongly changed their partner preference, indicating that the fly's peripheral nervous system is essential for pheromonal detection and mate choice.