A significant decrease in lysosomal as well as in the total activity of cathepsin B during fasciolosis was also observed (by about 18%, 23%, and 15% for lysosomal and by about 40%, 42%, and 25% for total in comparison with control group in the 4th, 7th, and 10th wpi, respectively). This evidence concerns the gene CTSB and fascioliasis.