ABSTRACT Mammals use pheromones to find mates, regulate reproduction, and organize social behavior. The identification of new pheromones, purified from natural sources, has repeatedly triggered new discoveries about the genes, cells, and circuits essential for social behavior. Recently, my lab identified two novel pheromones present in male mouse urine. These pheromones play an essential role in at least one behavior, the acceleration of puberty in juvenile females. However, several features of these new pheromones, and the responses of the neurons that detect them, suggest an even wider role. Structural clues present in these new compounds hint at a previously-unsuspected mechanism for their detection involving multiple sensory systems, receptor genes, circuit mechanisms, and metabolic pathways. We propose to (1) determine whether a multisensory complex involving both volatile and nonvolatile cues coordinate the discovery, detection, and recognition of these vital cues, (2) identify the receptor genes involved in their detection and consequent behaviors, and (3) test whether stereotyped circuit features contribute to the production and plasticity of suitable behavioral responses. We believe that the new opportunities afforded by these novel pheromones will provide new tools to probe fundamental mechanisms regulating mammalian physiology and behavior.