Abstract: (1) The hookworm larvae which had been immersed in the extract of the mouse's, skin smeared with 0.5% or 1.5% levamisole (LVM) lost the ability of skin penetration; (2) After 1.5% 3H-LVM had been applied onto the belly skin of the mouse the drug radioactivity in the skin decreased rapidly in the first 3 days, but 3 days later, the speed became distinctly slower. After 4-5 weeks, a certain amount of the drug could still be detected. The drug was centered mostly in the applied part of the skin, increased with increasing dosage and was far much higher by cutaneous administration than by oral route. It was suggested that the continued effect of LVM in preventing hookworm larvae infection was due to the drug remaining in the skin for a relatively long time.