Schistosome egg granulomas in the livers of thymus-intact (nu/+) mice are large and contain eosinophils and mast cells, while those in nude athymic (nu/nu) mice are small and devoid of eosinophils or mast cells. To investigate the cell sources and cell kinetics of hepatic granulomas of nu/+ mice isolated and grafted into the skin of nu/nu mice, biopsies taken after grafting were examined by light and electron microscopy and autoradiography after 3H-thymidine (TdR) injection of either the donor or recipient mice. At 1 week, the grafted granulomas appeared to be amorphous and were surrounded by leukocytes, and the 3H-TdR-labeled donor cells had disappeared. After 2 weeks, repopulation with macrophages began and by 3-5 weeks, the granulomas morphologically resembled hepatic lesions of nu/+ mice. Injection of recipients with 3H-TdR before grafting, showed that labeled macrophages, eosinophils, and mast cells repopulated in granulomas. No granulomas were seen when nu/nu mice were grafted with schistosome eggs alone, and organ culture of nu/+ granulomas before grafting reduced the number of repopulated granulomas. These findings indicate that nu/+ cells in grafted granulomas are replaced by nu/nu cells. Granulomatous reaction of the grafted sites in nu/nu mice is influenced by a substance in nu/+ granulomas, and cells of nunu mice locally acquire a nu/+ type response.