Background: Trichophyton mentagrophytes is a complex species and 3 perfect states, Arthroderma benhamiae, A. vanbreuseghemii, and A. simii have been described. In Korea and Japan, all of the isolates of T. mentagrophytes of which the perfect states determined were known as A. vanbreuseghemii till recently. However, in Japan, one isolate from a monkey was reported as A. simii and several strains from rabbits or patients were A. benhamiae. Therefore, it is necessary to confirm the existence of A. simii or A. benhamiae in Korea. Objectives: We performed this study to determine the teleomorphs of 19 strains of T. mentagrophytes isolated from Korean patients infected from pets and 4 from the skin lesions of rabbits. Metbods: DNA sequences of internal transcribed spacer 1 (ITS1) area of the 23 isolates and 3 reference strains were determined and matched with the data registered in GenBank nucleotide sequence database. Results: The sequencing data of 22 isolates were very similar to those of A. vanbreuseghemii and 1 to T, mentagrophytes var. interdigitale respectively. Conclusion '. Although all of the clinical isolates were related with A. vanbreuseghemii in this study, the possibility of the existence of A. simii and A. benhamiae in Korea is still high and further study is needed. (Korean J Dermatol 2001;39(8): 1086-1093)