The presence of eosinophils in the conjunctival epithelium is indicative of allergies, and detection is currently performed by cotton swab scrapings. Although mast cells are thought to be chemotactic for eosinophils and thus presage their accumulation, the former's use as early indicators of allergy has heretofore been hindered by poor detection methods. The recent development of a special brush now makes it possible to collect many cells with less disturbance of the conjunctival epithelium. In the present study, we have used this brush for conjunctival scraping in 18 patients with vernal and allergic conjunctivitis, and 10 patients serving as controls. The superior and inferior tarsal conjunctiva in both eyes were examined, and the specimens were stained using Hansel's method. Mast cells were observed in at least one of the tarsal conjunctivae in all cases of vernal and allergic conjunctivitis, whereas eosinophils were so observed in only eight cases (44.4%). Neither mast cells nor eosinophils were present in the conjunctivae of the normal group. Although treatment by mast cell stabilizers produced clinical remissions, they induced disappearance of mast cells in only 10 cases (55.6%), whereas in six cases (33.3%) the mast cells increased, and in two cases they were unchanged (11.1%). Six cases (33.3%) each showed disappearance of, increase in, and no change in eosinophils, reflecting even less of a response of these allergic cells to the treatment. The presence of mast cells and eosinophils, as determined by our cytologic method, was found to be correlated with the early detection, but not the clinical severity, of allergic conjunctivitis.