Ten cases of cystic echinococcosis and ten cases of alveococcosis were treated with albendazole in dosage of 20 mg/kg/d x 30 days for 10-32 courses. All cases were followed up 10 months to 5 years (average 26 months). 7 of 10 cases of cystic echinococcosis and 7 of 10 cases of alveococcosis showed reduction in size of lesions in the liver and lung shown by B ultrasonography and chest X-ray films. 3 cases of cystic echinococcosis of liver operated during the treatment course showed that all the daughter cysts were collapsed and mostly were necrotic and liquefied. Apparently albendazole is effective for the treatment of inoperable cases of hydatidosis.