Compound 48/80 (N-methyl-p-methoxyphenethylamine formaldehyde condensation product) was used to selectively degranulate mast cells to induce conjunctival eosinophilia in 12 rabbits. Biopsy specimens of bulbar conjunctiva showed that eosinophils were present in all treated eyes. With repeated treatments the number of eosinophils increased; these cells were concentrated in the subepithelial and epithelial zones by day 3. Eosinophils were not found on scrapings of the bulbar conjunctiva in 75% of the rabbits that received single or multiple treatments. We conclude that deep and superficial eosinophil infiltration may be present even when eosinophils are not seen on conjunctival scrapings. Therefore, the absence of eosinophils in scrapings should not rule out the diagnosis of ocular allergy.