Anidulafungin (LY-303366, V-echinocandin trade mark, Vicuron Pharmaceuticals, Inc.) is a new echinocandin antifungal agent with broad spectrum activity against Candida and Aspergillus spp. Anidulafungin exhibits low toxicity, concentration-dependent fungicidal activity for Candida, and a prolonged post antifungal effect (> 12h). In vitro activity demonstrates excellent potency and spectrum versus azole-susceptible and -resistant Candida spp. and a low minimum effective concentration for Aspergillus spp. In vivo anidulafungin is fungicidal against Candida in neutropenic animal models of disseminated candidiasis. Against Candida anidulafungin exhibits concentration-dependent killing and clearance of residual fungal burden in target organs (liver, lung, spleen, kidney) and plasma/tissue concentrations exceed the minimum inhibitory and minimum fungicidal concentrations of the infecting organism throughout the dosing interval. Although the activity of anidulafungin in animal models of pulmonary or disseminated aspergillosis shows increased survival and improvement in the pulmonary infarct score, the effect on residual fungal burden and Aspergillus antigenemia determination does not indicate in vivo fungicidal activity. It seems that the major effect of anidulafungin and other echinocandins in vivo against Aspergillus spp. is the decrease in the angioinvasive potential of the organisms. Clinically, anidulafungin has been shown to be safe and effective in the treatment of oesophageal candidiasis and candidemia. Further clinical application of this new antifungal agent is warranted.