The mechanisms of late phase allergic reaction (LAR) have been investigated by many researchers in the past decade, since LAR was recognized clinically to be more important than early phase allergic reaction (EAR). The selective eosinophil recruitment in LAR can be explained by the hypothesis of the cascade of cytokines and adhesion molecules. Since cytokines were initially identified as the factors derived from activated T cells, T cells were thought to play an important role in the LAR in the late 1980s. In 1989, murine mast cells were reported to produce many cytokines following activation through Fc epsilon R I. The current topic is to clarify which cell type mainly induce LAR either CD4+ T cells or mast cells.