The paraoxonase (E. C. 3.1.1.2.) is a major enzyme to detoxicate the organophosphorus and carbamate which are the most widely used as the agricultural spraying insecticides. To investigate the distributions of plasma paraoxonase activity and the fators affecting the enzyme activity, the plasmas of 945 Korean rural population were analyzed with the modified Krisch's direct sphectro;hotometry method. Three indices of the enzyme activity-basal activity, stimulated activity (by NaCl), % stimulation -were obtained from the analysis. Three indicies suggested unimodal distributions, so we couldn't identify the low activity group; risk group to organophosphorus & carbamate insecticides poisoning. There is no significant relation between 3 activity and the stimulated activity have significant relationship and high coefficient of determination with the activities of their parents (r2=0.30, 0.24; p<0.05), but the % stimulation does not (r2=0.02; p<0.05). These results suggest that the activity of paraoxonase is determined mainly by the genetic factor.