A population of bank voles (Clethrionomys glareolus) and wood mice (Apodemus sylvaticus) inhabiting an oak wood in Somerset was examined for dermatophytes at monthly intervals for 2 years. The marked animals were frequently retrapped, allowing a study of host fungus relationship over a period of time. Microsporum persicolor (Sabouraud) Guiart er Grigorakis and Trichophyton mentagrophytes (Robin) Blanchard were isolated from both animal species, but M. persicolor predominated in bank voles and T. mentagrophytes in wood mice. In their most favoured host, both dermatophyte species often persisted for several months, but in the less favoured host they were never isolated at more than one sampling. Males of both animal species were infected more often than females. The existing evidence for the geophilic nature of both fungi is reviewed and shown to be very weak, especially for M. persicolor. This is the first report from Great Britain of T. mentagrophytes infection of wood mice not in contact with human habitation.