The aim of the study was to examine the effect of diazinon and carbaryl, and validate the efficiency of a modified electrometric method in measuring cholinesterase activity (ChE) in rabbits. Oral administration of female rabbits with diazinon at 35 mg/Kg, and with carbaryl at 500 mg/Kg, induced signs of toxicosis characteristic of cholinergic over stimulation. The signs were associated with significant decreases of plasma, erythrocyte and brain ChE activities with diazinon, but with carbaryl there were only significant decreases of plasma and erythrocyte ChE activities in comparison with control values. The extent of ChE inhibition in the erythrocyte correlated well with that of the brain in diazinon treated rabbits. The results suggested that the described electrometric method is simple, accurate and efficient in measuring the ChE inhibition caused by diazinon and carbaryl insecticides in rabbits.