Interleukin 4 (IL-4) may play a role in the development of allergic disease. We questioned whether IL-4 related phenomenon occurred on the surface of the conjunctiva during allergic conjunctivitis. Ten patients with cedar pollen-allergic conjunctivitis and 10 patients with postsurgical conjunctivitis were enrolled in this study. Cells were collected by brush cytology from the upper palpebral conjunctiva. After the cells were cultured for 24 hours, the levels of IL-4, IgE, and histamine were measured in the supernatants. An ELISA was used for histamine and a highly sensitive sandwich ELISA for IL-4 and IgE. Conjunctival cells were also stained and fixed by May-Grunwaids stain solution. The number of superficial cells, especially lymphocytes, were compared in the two groups. The total number of cells collected by brush cytology did not differ in allergic vs., postsurgical conjunctivitis. Lymphocytes were similarly present in such specimens. The levels of IL-4 (p = 0.01) and histamine (p = 0.02) significantly increased in the specimens from patients with allergic conjunctivitis, although IgE was not detected in both groups. There was a correlation between the level of IL-4 and histamine (p = 0.0001). Conjunctival cells in allergic conjunctivitis produced a larger amount of IL-4 and histamine for cedar pollen compared to the postsurgical conjunctivitis. As with other allergic diseases, IL-4 may play a role similar to that of histamine in the development of allergic conjunctivitis.