Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) of Echinococcus granulosus cyst wall harbored in mice for 10-12 months was measured. The activities of the 2 enzymes were 3,430 +/- 1,370-4,160 +/- 1,790 and 1,560 +/- 840-2,890 +/- 1,470, respectively. When infected mice were treated ig with mebendazole (Meb) 25 mg.kg-1.d-1 for 7-14 d, or 50 mg.kg-1.d-1 for 7 d, the ALT activities of cyst walls of both collapsed and full cysts were inhibited significantly with average inhibition rates of about 50%. Another benzimidazole derivative, albendazole (Alb), also inhibited ALT activity of the cyst wall with an inhibition rate of 40.7%, but this was not the case in the treatment with praziquantel 500 mg.kg-1.d-1 of the infected mice for 14 d. When the infected mice were treated ig with the above mentioned drugs at the same regimens, no apparent effect on AST activities of the cyst wall was seen except for the group treated ig with Meb at a higher daily dose, the inhibition rates being 26% (collapsed cyst) and 43.9% (full cyst). The significance of the results has been discussed briefly.