The B mating type of Schizophyllum commune is defined by a multi-specific pheromone/receptor system. The interaction of pheromone receptors and their ligands, encoded by the Balpha locus, triggers sexual development. The receptors belong to the family of G protein-coupled seven-transmembrane-domain receptors, while the ligands are small lipopeptide pheromones. A productive interaction is only possible between molecules derived from different specificities. There is no induction of sexual development by pheromones of self-specificity. Since there are nine versions of different specificity for pheromones and receptors in Balpha, this system can be used to study multi-ligand discrimination. We investigated pheromone discrimination using chimeric receptor molecules and the influence of single point mutations on activation profiles of the receptor.