This article overviews the emerging problem of antifungaldrug resistance in Aspergillus. Fluconazole and ketocona-zole (KCZ) are inactive against Aspergillus. Validation oftesting procedures for the detection of itraconazole (ITZ)resistance in Aspergillus fumigatusin 19971,2were furthervalidated with posaconazole (SCH-56592)3,4and voricona-zole (VCZ)5(Hitchcock, personal communication). Work isongoing to validate testing procedures for azoles innon-fumigatus Aspergilli.In contrast to the successful validation of azole suscep-tibility testing ofAspergillus, successful validation ofamphotericin B (AmB) testing has been problematic, withthe probable exception ofAspergillus terreus.6,7This article summarizes data from our laboratory, con-trasts it with that in the literature, and makes recommen-dations for subsequent work to further clarify thesituation. The new group of antifungal drugs, the can-dins, is not discussed and information on terbinafine istabulated only for comparison. Resistance in flucytosine is also not discussed.