IN 1947, three strains of Microsporum were isolated from the scalp of an adolescent girl with tinea capitis. The infection was noteworthy for its resistance to therapy and for the joint occurrence of Microsporum audouini and Microsporum canis. 1 The strains were named A, B and C. A and B were identified, in accordance with accepted technics and criteria, as M. canis, and C as M. audouini. They were repeatedly subcultured and transplanted and were observed, for more than a year, for rate of growth, configuration of surface, development of pigment and presence of spindle-shaped macroconidia or fuseaux on mounted culture slides. This paper presents the results of the examination of all cultures for the presence of fuseaux and discusses the significance of these findings. Data relating to the gross appearance of the strains are not relevant to this presentation. METHOD The fungi were grown on dextrose-peptone agar