RÉSUMÉ
Serum cholinesterase (ChE) level has been used as an indicator for an exposure to organophosphorus and carbamate insecticides by showing a lower level than normal people. Normality serum ChE level may vary depending on sex, age and occupation. The serum of 568 blood donors at Maharaj-Nakorn Chiang Mai Hospital was collected to study the variation of ChE level among different occupations, sex and age. Enzyme ChE activity was measured using butyrylthiocholine as a substrate and dithiobisnitrobenzoate as a chromophore. The results showed that an average ± SD level of serum ChE in those of blood donors was 6,043 ± 1,247 U/L. There was no significant different in mean serum ChE level between group of monks (n=13), unemployees (n=16), traders (n=25), soldier and policemen (n=102), civil services (n=35), employees (n=195) and students (n=75) at 95% confidence. But in farmers (n=107), the serum ChE level appeared to be lower than in other occupational groups. Furthemore, there was a significant different in serum ChE level between females and males which show mean ± SD ChE activities at 5,421 ± 1,104 U/L (n=65) and 6,123 ± 1,243 U/L (n=503) respectively. However the ChE level in different age groups were not significantly different in this study.