Anidulafungin is a new semisynthetic echinocandin with antifungal potency. IC50 & Target: Antifungal^[1] In Vitro: Anidulafungin (LY-303366) has MICs of ≤0.32 μg/mL for all Candida albicans (n=99), Candida glabrata (n=18), and Candida tropicalis (n=10) isolates tested. Anidulafungin is also active against Aspergillus species (minimum effective concentration at which 90% of the isolates are inhibited, 0.02 μg/mL) (n=20), is less active against Candida parapsilosis (MIC at which 90% of the isolates are inhibited [MIC90], 5.12 μg/mL) (n=10), and is inactive against C. neoformans (MIC90 >10.24 μg/mL) (n=15) and B. dermatitidis (MIC90, 16 μg/mL) (n=29).The MICs of Fluconazole for three strains of C. tropicalis, seven strains of C. glabrata, and two strains of Candida krusei are ≥16 μg/mL. The MICs of Anidulafungin for 11 of these 12 strains range from 0.08 to 0.32 mg/mL. The twelfth strain is a C. krusei strain (Fluconazole MIC, 32 μg/mL) for which the Anidulafungin MIC is 1.28 mg/mL. The MIC at which 90% of the isolates are inhibited (MIC90) for these 12 strains is 0.32 μg/mL. The Anidulafungin MIC90 for the remaining 18 C. glabrata isolates and C. tropicalis isolates for which the Fluconazole MICs are ≥ 8 μg/mL is also 0.32 mg/mL. Anidulafungin appeares equally active against Candida species for which the fluconazole MICs are ≥16 mg/mL and against those for which the fluconazole MICs are ≥ 8 μg/mL. Anidulafungin has significantly less activity against C. neoformans and B. dermatitidis than against C. albicans, C. glabrata, and C. tropicalis. Ketoconazole and amphotericin B are the most active antifungal agents tested for both C. neoformans and B. dermatitidis. Anidulafungin demonstrated potent in vitro activity against Aspergillus species with a MEC90 of 0.02 μg/mL. MICs of Anidulafungin for the control strain yeast isolates are 0.02 μg/mL for C. albicans ATCC 90028, 0.16 mg/mL for C. glabrata ATCC 90030, and >10.24 μg/mL for C. neoformans ATCC 90112^[1]. Strains selected with CD101 that have a 2-fold or greater CD101 MIC increase also have at least a 2-fold MIC increase for Anidulafungin (ANF) and/or Caspofungin (CSF)^[2].