To elucidate the mechanism of ocular surface allergic disease, we focused on IL-4, which is one of the key factors in regulating IgE production, and thus determined the concentration of IL-4 in tears. IL-4 concentration was determined in the tears of 15 patients with seasonal allergic conjunctivitis, 15 vernal keratoconjunctivitis (VKC), 10 giant papillary conjunctivitis (GPC), 10 patients with non-allergic conjunctivitis and post-cataract surgical conjunctivitis as intermediate conjunctivitis, and 10 normal subjects using a highly sensitive sandwich ELISA. The mean level of IL-4 in normal controls was low, and seasonal allergic conjunctivitis, VKC and GPC showed a significant elevation (P < 0.05), respectively. IL-4 of VKC and GPC were also significantly higher than allergic conjunctivitis, and non-allergic conjunctivitis and post-cataract surgical conjunctivitis were not higher than normal. These results raise the possibility that the increased level of IL-4 in tears could play a role in allergic disease and its severity in patients.