Nine patients with complicated hydatid disease managed with surgery and mebendazole/albendazole are presented. Five patients received albendazole (1 treatment course) and 5 patients received mebendazole (3 had 2 treatment courses, 1 had a switch-over from mebendazole to albendazole). The mean durations of treatment and follow-up were respectively 7 +/- 2.5 months and 7 +/- 2.5 months (albendazole); 13 +/- 10 months and 29 +/- 31 months (mebendazole). A superior clinical and radiological response was seen in 1 patient with disseminated intra-abdominal disease on switching therapy from mebendazole to albendazole. Radiological improvement occurred in 3/5 courses of albendazole and in 2/8 courses of mebendazole. Clinical improvement occurred in 3/5 courses of albendazole and 0/8 courses of mebendazole. Radiological deterioration was demonstrated in 0/5 courses of albendazole and 2/8 courses of mebendazole. Although the impression was that albendazole was superior, good responses were also seen with mebendazole. The heterogeneity of the patients, their disease, short follow-up time, lack of more sensitive noninvasive assay techniques urges caution before firm conclusions can be drawn.