The performance of the dermatophyte test medium (DTM) RapidVet-D was assessed using hair samples collected from experimentally infected guinea pigs. Three dermatophyte species were included in the study: Microsporum canis, Trichophyton mentagrophytes and Trichophyton equinum. DTM substrates were inoculated with infected hairs and scales, incubated at 18, 21, 24, 27 or 37 degrees C and examined daily for 15 days. The rapidity of colour change was clearly related to the incubation temperature and to the number of infected hairs deposited on the reactive substrates. With the optimum incubation temperature 27 degrees C, a systematic colour change could be observed only a few days post-inoculation: 3 days with M. canis infected hairs, 4 days with T. equinum and 5 days with T. mentagrophytes.