Eight patients with hydatidosis treated with albendazol in daily doses of 10 mg/kg daily in courses of 28 days (4-6 courses) were analysed. The patients came from Morocco, Spain, Turkey and Yugoslavia. Seven patients had a cyst (or cysts) in the liver and one had also cysts in the kidneys. One patient had cysts in the muscles of the extremities. As assessed by ultrasonic scanning, computed tomography of the cysts, general condition, serology and the presence of hydatid antigen in the serum, treatment was effective in six patients. One patient developed an allergic reaction to albendazol. All of the patients had varying degrees of liver involvement which were reversible. Neutropenia did not occur. Various parameters for assessing the therapeutic effect are mentioned. Albendazol appears to be effective in the treatment of non-operable hydatid disease and to prevent recurrence after surgery.