Coumaphos (8 or 15 mg/kg of body weight), triflupromazine HCl (1.1 mg/kg of body weight), or isotonic saline solution were given to 8 groups of sheep (5 per group) fed a low-or normal-dietary protein ration. One set of clinical signs, mortality rate, mean survival time, necropsy lesions, and plasma and erythrocyte cholinesterase (ChE) activity were monitored for each group. Observations suggested potentiation effect between the administered compounds. Inhibition of ChE activity was enhanced in groups given both drugs. Feeding of low-dietary protein ration adversely affected the development of clinical signs, mortality rate, mean survival time, and ChE activity. Recovery of ChE activity of triflupromazine HCl-treated animals was faster than in their respective controls, and sheep fed normal-dietary protein ration had faster ChE recovery than those fed the low-dietary protein ration. Inhibition of erythrocyte ChE found was a better index of organophosphorus toxicosis than that of plasma ChE.