Eosinophil chemotactic factor (ECF) was detected in the culture supernatant of isolated intact egg granulomas from the livers of Schistosoma japonicum-infected mice. This factor had an apparent molecular weight of 15,000 by high-pressure liquid chromatography with an SW3000 column and bound to concanavalin A-Sepharose 4B. When cells obtained by enzymatic digestion of isolated granulomas were cultured under the presence of soluble egg antigen of S. japonicum or concanavalin A, ECF was also detected in the conditioned medium. The physicochemical nature of the ECF produced by concanavalin A-stimulated granuloma cells was similar to that produced by isolated intact granulomas. The ECF-producing activity of the cells was abolished by pretreatment with anti-Thy-1.2 or anti-Lyt-1.2 monoclonal antibody and complement but not by anti-Lyt-2.2 antibody. Furthermore, nylon wool-passed, T-enriched granuloma cells required collaboration of syngeneic macrophages to produce ECF. These results suggest that Lyt-1-positive T cells in the granuloma could, in collaboration with macrophages, produce ECF and thereby attract eosinophils to this lesion.