A loop ligated at both sides was made in the ilecoecal portion of rabbit intestine. As2O3 solution was infused into this loop and the blood circulating around this loop was collected from the cannulated vein. As2O3 content absorbed in blood as well as that remaining in this loop were determined. In control rabbits on no drugs, approx. 30% of As2O3 infused was absorbed into the blood in 60 minutes. However, in rabbits on parenteral dimercaprol (BAL) or thioctic acid (TA), the content of As2O3 absorbed into the blood decreased remarkably while the content of As2O3 remaining in the loop increased. On the other hand, even when BAL or TA were added directly into thip loop containing As2O3, the content of As2O3 absorbed in blood decreased markedly, compared with that of the control group. Thus it was demonstrated that BAL or TA combined with AsO3(3-) after being excreted into the intestinal tract from the bile-duct, bringing about inhibition of the enteral absorption of As2O3.