Albendazole was administered preoperatively to two patients with active alveolar hydatid disease for 58 and 84 days. Vesicles of larval Echinococcus multilocularis obtained from surgical tissues were inoculated into red-backed voles for in vivo testing viability. No proliferation of the larval cestode had occurred when the animals were dissected three months post-inoculation. These findings suggest that short-term therapy with albendazole was effective in killing the larval cestode in these two cases. Albendazole was found to be hepatotoxic but resulting transaminase abnormalities have been reversible. Close monitoring of liver function and hematology is essential in patients under albendazole therapy.