Guinea pigs infected with Trichophyton mentagrophytes developed a cutaneous fungal lesion and became skin test positive to fungal antigen (trichophytin). The cutaneous fungal lesion, while thought to be a cell-mediated response, differed histologically from the skin test site. Basophils were not demonstrated in biopsies of cutaneous fungal lesions, whereas basophils were numerous in biopsies of trichophytin skin test sites. When sensitization to trichophytin was accomplished by injection of hypha in complete Freund's adjuvant instead of infecting with live fungus, basophils could not be demonstrated in skin test sites. This report demonstrated that guinea pigs could be primed for cutaneous basophilic hypersensitivity (CBH) responses by infection with live fungus.