Two patients with inoperable multiple Echinococcus granulosus infections involving the lungs and the liver (one patient) were treated with the following daily doses of mebendazole (Vermox): 3 days 1000 mg, 3 days 1500 mg, the following 3 months 30-40 mg/kg body weight. One of the patients had been treated before with mebendazole in similar doses for 3 periods of 5-6 weeks each. The patients received the drug as 500 mg tablets divided into 3 daily doses after meals. After termination of treatment a distinct regression of lung cysts was demonstrable in both patients, with the exception of one cyst. The liver cyst in one of the patients had also decreased in size. About 8 months after therapy signs of reactivation of lung cysts were observed in one patient, and a new course of mebendazole treatment was therefore started.