Stereotypic behaviour, such as territorial calls and songs, is thought to be evolutionarily conserved, and therefore useful in discerning systematic relationships. We examined vocalizations of several species of Peromyscus and Onychomys, a monophyletic group of rodents (Peromyscini). We report stereotypic vocal signals occurring in both sexes of the deer mice Peromyscus californicus, P. eremicus, P. leucopus, P. melanophrys, P. polionotus, and the grasshopper mice Onychomys arenicola and O. leucogaster. The stereotypic vocalizations of P. eremicus, P. leucopus, and P. polionotus are confined to frequencies greater than 20 kHz, unlike those of Onychomys, which are clearly audible, or P. californicus and P. melanophrys, which generate lower frequency vocalizations than the other Peromyscus. We did not observe stereotypic vocalizations in P. aztecus. Intensity, context and consistency suggest that these vocalizations serve an announcement function. Distribution of spectral energy distinguishes genera and most species, and some use of frequency is correlated to body size. There is a dichotomy between Onychomys and Peromyscus in the use of frequency, a genus-specific pattern identified previously among other peromyscine lineages.