Paraoxonase-1 is an esterase enzyme and it has 3 types of activity, namely paraoxonase, arylesterase, and diazoxonase. It has been reported that paraoxonase-1 deficiency is related to increased susceptibility to development of atherosclerosis and cardiovascular disease. The aim of this study was to investigate serum paraoxonase and arylesterase activities in children with iron deficiency anemia and vitamin B-12 deficiency anemia. Thirty children with iron deficiency anemia, 30 children with vitamin B-12 deficiency anemia, and 40 healthy children aged 6 months to 6 years were enrolled in this study. Serum paraoxonase and arylesterase activities were measured with a spectrophotometer by using commercially available kits. Mean paraoxonase and arylesterase activities in vitamin B-12 deficiency anemia group (103 +/- 73 and 102 +/- 41 U/L, respectively) were significantly lower than mean activities of control group (188 +/- 100 and 147 +/- 34 U/L, respectively; P < .001 for both) and iron deficiency anemia group (165 +/- 103 and 138 +/- 39 U/L, respectively; P < .05, P < .001), whereas there were no significant differences between iron deficiency anemia and control groups (P > .05). Paraoxonase and arylesterase activities significantly increased after treatment with vitamin B-12 in vitamin B-12 deficiency anemia; however, there were no significant changes in the activities of these enzymes after iron treatment in iron deficiency anemia group. Important correlations were found between vitamin B-12 levels and both paraoxonase and arylesterase activities (r = .367, P < .001; r = .445, P < .001). Our results suggest that vitamin B-12 deficiency anemia causes important reductions in paraoxonase and arylesterase activities, and after vitamin B-12 therapy the activities of these enzymes returned to near-normal levels.