The effects of recombinant human (rh) interleukin(IL)-4 or rhIL-13 on survival, and chemotactic activity of humaneosinophils were examined. OnlyrhIL-13 prolonged eosinophil survival in a dose-dependent manner above 3 ng/ml. Eosinophil survival induced by rhIL-13 was inhibited by monoclonal antibodies (mAbs) against IL-3 (p< 0.0!) and granulocyte-macrophage colony-stimulating factor (GM-CSF)(p< 0.05), suggesting that rhIL-13 induced IL-3 and GM-CSF production from eosinophils and an autocrine mechanismis responsible for the eosinophil survival. Theeffects of rhIL-13 on eosinophil chemotactic activity were also examined. rhIL-13 showed chemotactic activity for eosinophils in a dose-dependent manner. Checkerboard analysis revealed that eosinophil migration was dependent on the concentration gradient, confirming that rhIL-13 is a chemotactic factor. rhIL-4 showednoeffects. IL-13 mayplay an important role in the survival andrecruitment of eosinophils in allergic diseases.(Internal Medicine 36: 179-185, 1997)