Protoscoleces of Echinococcus granulosus were cultured in vitro in 500, 250 or 100 micrograms/l albendazole sulphoxide for 1,3,7,10,14d and then 'rescued' (R) into drug-free medium for the remainder of the culture period. Successful minimum lengths of therapy were much longer than for praziquantel, and only at 500 micrograms/l was the 10dR treatment as effective as continuous therapy for 28d. Treatment with 100 micrograms/l both in continuous culture and in the 'R' experiments was ineffective over a 35d period. The results are compared with those from similar experiments using praziquantel.