For the purpose of elucidation the effects of MEA on the prevention and therapy of lead poisoning, the present experiment was conducted. The author first induced lead poisoning in rats and guinea pigs by administering them lead and measured quantitatively the changes occurring in the lead contents of blood, liver, kidneys, and femur in the rats and also the lead quantity excreted in urine of the guinea pigs, after administering to these animals. In addition, by administering Ca-EDTA to similar groups of animals treated in the same manner, the author compared the changes brought about by these two drugs and thus evaluated the effects of MEA. 1. At the end of the first week after repeated administration of MEA the changes in the lead contents in blood did not differ greatly from those observed in the control group, whereas those in the group repeatedly administered with Ca-EDTA showed extensively higher value. Those in the organs mentioned above did not differ greatly from each others among these three groups. 2. The lead contents in the organs 4 weeks after repeated administration of MEA did not differ from those in the control, but the contents showed the greater value of 2-3 times than the contents in the groups of repeated administration of Ca-EDTA. 3. It has been observed that the quantity of lead excreted in urine by MEA administration increases slightly as compared with that in the control group, but this increase is far lesser than that brought about by the Ca-EDTA administration. 4. From these it has been clarified that hardly any effect of dissolution and excretion of lead outside the body can be expected by the repeated administration of MEA, and that in this respect the effect of MEA is far inferior to that of Ca-EDTA.