Abstract: Pathological changes in alveolar hydatids from experimentally infected gerbils were studied after administration of albendazole or yquiton.The animals were divided into several groups including the control one,and drugs of different dosages were given separately to different groups with diverse durations of infection.According to the microscopical observation,the hydatids could be categorized into 3 grades:grade Ⅰ,degenerated cysts;grade Ⅱ, stable cysts (showing no proliferation);gradeⅢ,proliferated cysts.Larger proportion of grade Ⅰ cysts were found in the group treated with albendazole at high dosage(33.3%)and the two groups treated with yquiton(25.0% and 16.3%).The proportion of grade Ⅰ cysts in gerbils with shorter duration (45 d) of infection was larger than those with longer duration(60 d).Lymphocyte infiltration to various extent was present surrounding the alveolar hydatid cysts in all the treated groups.More marked infiltration of lymphocytes was observed in albendazole treated gerbils(106.9±34.3 300.1±59.5)( P 0.001).However,the combined medication of albendazole and yquiton was less efficacious.