The mating pheromone response pathway in Saccharomyces cerevisiae is one of the best understood signalling pathways in eukaryotes. Comparison of this system with pathways in other fungal species has generated surprises and insights. Cloning and targetted disruption of genes encoding components of the pheromone response pathway has allowed the attribution of specific functions to these signal transduction components. In this review we describe current knowledge of the Kluyveromyces lactis mating system, and compare it with the well-understood S. cerevisiae pathway, emphasizing the similarities and differences in the heterotrimeric G protein activity. This mating pathway is controlled positively by both the G alpha and the G beta subunits of the heterotrimeric G protein.