[en] Almost 100% of 7- to 10-day-old Hymenolepis diminuta became established when surgically transplanted from donor mice into the duodenum of naive recipient mice. Transplanted tapeworms survived 8 to 12 days, by which time they had survived much longer in total than they would have done in the donor. Mice previously immunized by a primary infection rejected transplants within 4 days. Sub-lethal irradiation (550 rad) delayed rejection by immune mice but such mice still rejected worms much more quickly than did naive mice. Surgery was shown to delay by 2 to 3 days the rejection of worms by naive mice, and the importance of circumventing surgery by administering the worms per os is emphasized. Prospects for reconstituting irradiated immune mice are considered vis-a-vis work with nematodes, and the differences which, on present knowledge, appear to exist between nematode and cestode rejection are briefly discussed. (author)