Abstract: The purpose of the present study was to apply a modified electrometric cholinesterase method for measurement of plasma and erythrocyte cholinesterase activities in subjects exposed to insecticides during their routine work. The subjects (n = 40) of both sexes were farmers (31) and veterinarians (9) from Mosul, Iraq and none was suffering from any overt health problems. A modified electrometric method was used to measure plasma and erythrocyte cholinesterase activities using 0.2 mL blood sample, 0.1 mL of 7.1% acetylcholine iodide as a substrate with incubation at 37°C for 20 min. Cholinesterase activities of the subjects were compared with reference values determined simultaneously. The percentage of plasma cholinesterase inhibition in the subjects (n = 23) ranged between 11-70% that comprised 10-20% inhibition in 14 subjects, 21-40% in 6 subjects and 41 to 70% in 3 subjects. Erythrocyte cholinesterase inhibition in the subjects (n = 18) ranged between 11-51% comprising 10-20% inhibition in 13 subjects, 21-40% in 4 subjects and 51% in one subject. The data suggest the value of the modified electrometric method for monitoring blood cholinesterase inhibition in workers exposed to insecticides and further stress the need for frequent blood cholinesterase monitoring programs to include a wider range of workers in Iraq occupationally exposed to anticholinesterase pesticides.