Commercial disinfectants classified as fungicides may not be effective against commonly encountered fungi within reasonable periods. Cell suspensions of clinical fungal isolates were exposed to use-dilutions of various disinfectants. Quaternary ammonium compounds, iodophors, and phenolics were not fungicidal against all test fungi within 60 min of exposure. Trichophyton mentagrophytes, Epidermophyton floccosum, and Aspergillus fumigatus were among the more resistant fungi. Disinfectants that possess low-level activity should not be used for disinfection of medical instruments that come in contact with the patient. The only reliable and safe measure is to use high-level disinfectants such as the glutaraldehydes, which are fungicidal in 15 to 30 min.