The urine of mice, rats and some other rodents contains substantial quantities of proteins that are members of the lipocalin family. The proteins are thought to be responsible for the binding and release of low molecular weight pheromones, and there is now good evidence that they discharge this role, providing a slow release mechanism for volatile components of scent marks. However, the proteins may function as chemosignalling molecules in their own right, contributing one or more roles in the communication of individual identity and scent mark ownership. In this review, we summarize current understanding of the structure and function of these urinary proteins, and speculate about their role as supporters or as key participants in the elaboration of the complex chemosensory properties of a rodent scent mark.