Two distinctive types of eosinophil chemotactic lymphokines (ECF-L) directed against eosinophils obtained from bone marrow (BM-Eo) or from peritoneal cavity (PEC-Eo) were isolated from the media conditioned by spleen cells from mice infected with Schistosoma japonicum by a combination of anion-exchange chromatography on DE52, affinity chromatography on Procion Red agarose, and high-performance liquid chromatography. The molecular weight of ECF-L directed against BM-Eo was 10,000 and that against PEC-Eo was 46,000 by SDS-PAGE analysis. After isolation, selectivity of the two distinct ECF-L was examined using BM-Eo, PEC-Eo and circulating Eo. ECF-L directed against BM-Eo could attract only BM-Eo, whereas that directed against PEC-Eo could attract not only PEC-Eo but also circulating Eo. Synthetic ECF-A was chemotactic against both BM- and circulating-Eo but not against PEC-Eo. When BM-Eo were cultured with ECF-L selective to PEC-Eo, they became reactive to ECF-L selective to PEC-Eo, whereas ECF-L selective to BM-Eo did not have such effect. These results suggest that ECF-L selective to PEC-Eo is not simply a chemo-attractant but also is important in eosinophil differentiation.