Summary111Indium‐oxine‐labelled rat eosinophils were injected i.v. into rats infected with Nippostrongylus brasiliensis and controls. Radionuclide imaging was done to measure the rate and extent of radioactive uptake into different regions of the body in vivo. Radioactivity appeared first in the lungs then in the livers and spleens. The distribution of radioactivity and parasites was studied by gamma counting, histology and parasite counts. In infected rats, increased amounts of radioactivity localized in the skin, lungs and small intestines during the dermal, pulmonary and intestinal stages of the disease. It was concluded that localization of radioactivity was closely related to the tissue distribution of migratory larvae and adult worms. This technique may be of value in measuring alterations in eosinophil distribution and tissue localization in vivo, especially in helminthic infections and other disease where many eosinophils accumulate in tiss