Migration and elimination of 75Se-labeled Schistosoma mansoni were studied in previously infected mice by means of autoradiography and worm recovery. As in control mice, there appeared to be little if any worm elimination in the skin of previously infected mice. In previously infected mice, there appeared to be some worm elimination in the lungs and in migration sites between the lungs and liver, though much less than would have been expected from previous studies. In two of three experiments most of the challenge worm elimination in previously infected mice, above the normal attrition level occurring in the controls, appeared to take place in the liver. In the third experiment, it appeared that all of the challenge worm elimination occurred after migration to the lungs, and at least one-third of it in the liver. It was also observed that the lung chop procedure recovered viable schistosomula much less efficiently from previously infected mice than from controls, indicating that the reduction in lung schistosomulum recovery overestimates the amount of lung and prelung killing that occurs in reinfected mice.