Caspofungin is the first in a new class of antifungal agents, the glucan synthesis inhibitors, that interfere with fungal cell wall synthesis. Caspofungin exhibited in vitro and in vivo efficacy against a wide range of fungi and yeasts including Aspergillus and Candida species. A complete or partial response to caspofungin therapy was seen in 40.7% of immunocompromised adults with invasive aspergillosis who did not respond to, or did not tolerate, other antifungal agents in a noncomparative multicentre study. Caspofungin was effective in patients with oropharyngeal or oesophageal candidiasis, according to the preliminary results of 2 randomised double-blind trials. Caspofungin was generally well tolerated in a multicentre noncomparative trial involving patients with invasive aspergillosis. One or more drug-related clinical adverse effects were experienced by 13.8% of caspofungin recipients (the most common were fever, nausea, vomiting and complications associated with the vein into which caspofungin was infused). The tolerability of caspofungin appeared to be better than that of amphotericin B and similar to that of fluconazole in double-blind, randomised trials involving patients with mucosal candidiasis.