Alveolar echinococcosis (AE) is a rare parasitic disease caused by Echinococcus multicularis and most commonly involves the liver. Early diagnosis is essential to improve the prognosis of patients with AE of the liver. Em18, an 18-kD diagnostic antigen from Echinococcus multilocularis, is highly specific and sensitive to detect AE. We previously reported that an enzyme-linked immunosorbent assay (ELISA) system using a recombinant Em18 antigen (RecEm18) was highly useful in the differential serodiagnosis of AE. In this report, we present seven AE patients who showed dynamic changes in RecEm18-ELISA values in the course of long-term follow up of albendazole (ABZ) chemotherapy, and/or resections of the liver or bone metastasis. All seven AE patients revealed positive values, over the cutoff level, of the RecEm18-ELISA before the treatments. The values in six patients fell below the cutoff level after the treatments, but the value in a patient with recurrence never fell below the cutoff level, and increased again. From these results, it seems that the RecEm18-ELISA is useful to evaluate the efficacy of treatment and predict recurrence in patients with AE. RecEm18-ELISA may be an important examination for: (a) the mass screening of AE in Japan, (b) the confirmative diagnosis of AE prior to surgical and/or chemotherapeutic treatments, (c) the follow up of AE patients after treatments, and (d) for deciding on the discontinuation of chemotherapy in patients with an appropriate response.