Antifungal agents can be classified by their site of action in fungal cells, which can have important implications for both efficacy and tolerability. Currently available agents include the polyenes, nucleoside analogs, and the azoles. With the exception of 5-fluorocytosine, all agents act by interfering with the structural or functional integrity of the fungal plasma membrane. However, the non-selective nature of this therapeutic target results in concomitant cross-inhibition (or toxicity) in mammalian cells. New compounds that interfere with the fungal cell wall--a target not present in mammalian cells--therefore constitute an important focus of current clinical research. Caspofungin, the first representative of a new class of antifungals that inhibit beta-(1,3)-D-glucan synthesis, exerts potent activity against Candida and Aspergillus spp. and appears to be generally well tolerated. This paper reviews the data on caspofungin.