The changes in cholinesterase (ChE) activity was studied in different tissues of normal and 60 days T. spiralis infected albino rats following treatment with Mintezol (5 mg/rat/day, for 5 days) and 5-fluorouracil-Endoxan (500 mg/rat/day--100 mg/rat/day, for 5 days). In normal rats, administration of either Mintezol or 5-fluorouracil-Endoxan provoked a general decrease in the ChE activity of the various rat tissues. Treatment of 60 days T. spiralis infected rats with Mintezol increased markedly the ChE activity of the brain, liver, gastrocnemius muscle and serum. Meanwhile treatment with 5-fluorouracil-Endoxan decreased the enzyme activity in the selected rat tissues. It can be concluded that treatment with Mintezol and 5-fluorouracil-Endoxan in trichinellosis represents a certain danger. This danger results from general inhibition of ChE activity which may cause accumulation of acetylcholine.