Caspofungin (CAS) is the first of a new class of antifungal agents, the echinocandins, that interfere with fungal cell wall synthesis by inhibition of glucan synthesis. Here, we report the results of 31 patients treated with CAS following allogeneic SCT. CAS was administered as a second-line agent to patients with invasive fungal infection (IFI) (n=15) or fever of unknown origin (n=16) who were recalcitrant to or intolerant of prior antifungal therapy. Unsuccessful first-line regimes included amphotericin B (n=17), liposomal amphotericin B (n=5), fluconazole (n=3), itraconazole (n=1), and voriconazole (n=2). All patients received concomitant immunosuppressive therapy for graft-versus-host disease. In 23 patients, cyclosporin A (CSA) and CAS were administered concurrently without any major side effects detected. Observed increases in GPT were not clinically significant. Normalization of serum creatinine and significant reductions in C-reactive protein were observed in response to CAS. Favorable outcome to CAS were documented in eight of 15 patients with IFI and in 15 of 16 patients with fever of unknown origin. CAS is a promising alternative in patients with IFI and fever of unknown origin in the setting of allogeneic SCT.