Trichophyton mentagrophytes is both zoophilic and a common causative organism in human dermatomycosis. Therefore this dermatophyte is widely used for experimental efficacy testing of antimycotic agents and their active ingredients. The use of the guinea pig as an animal model for dermatomycosis is based on the predisposition of this species to spontaneous dermal fungal infections. A previously described guinea pig model was modified according to the results of pilot experiments. The modification consists of 1) evaluation of the infectious activity of the primary mycotic tissue cultures obtained from patients and 2) the efficacy testing itself with treatment of the infected skin area including the continuous clinical observation for 28 days. At first the required duration of cultivation and the number of spores for a reproducible infection of all animals were determined. The following efficacy test consisted of four groups with ten animals each. Group I (control of infection) remained without further treatment after experimental infections, groups II-IV received a single treatment by spraying at the day of infection with isopropanol (70%) (negative control), water (mechanic control) and the antimycotic agent (treated group), respectively. After 28 days under continuous examination, clinical symptoms (scabs; reddening, scaliness) were statistically analyzed. The model takes into account the duration and severity of infection in order to evaluate the differences between the four groups. The experimental protocol presented allows the efficacy of antimycotic agents to be demonstrated by means of statistical analyses. As an example the results of a successful prophylactic treatment against T. mentagrophytes with the antimycotic prophylactic Laudamonium (1%) are presented.