Single-cell physiology and cloning efforts have extended studies of the vomeronasal organ to cellular and molecular levels. Recent work has shown that transduction in the vomeronasal organ is probably mediated by signalling pathways distinct from those that mediate transduction in the main olfactory system. An advance in understanding transduction has come with the cloning from rat vomeronasal organ of a family of putative pheromone receptor genes that bear no sequence similarity to previously cloned receptors. Other work has examined the expression of putative signalling components and found a zonal organization of the epithelium. Patch-clamp studies have described the basic electrical properties of vomeronasal neurons and explored second-messenger pathways.