A cellular late-phase reaction is described in a rat model of topically induced ocular anaphylaxis. Rats were immunized with dinitrophenylatedAscaris suunextract and alum and were tested for active cutaneous anaphylaxis on day 13. Rats with a strong skin test response were selected for ocular challenge with di-DNP-lysine. Macroscopic observation and histologic evaluation were performed at 1, 6, and 24 h. In rats showing a moderate macroscopic ocular response at 1 h, mast cell degranulation was significantly increased at 1 h; no significant increase in eosinophils, neutrophils or lymnhocytes was found in the conjunctiva of these animals. In rats showing a marked macroscopic ocular response at 1 h, mast cell degranulation was significantly increased at 1 and 6 h; the number of eosinophils was significantly increased at 1 and 6 h, and of neutrophils at 6 h only. At 24 h, neutrophils and eosinophil numbers returned to baseline levels. There was no macroscopic evidence of a late-phase response in either group of animals. Our results suggest that, in keeping with earlier observations in human skin, a strong early response to antigen is required for the development of a late-phase ocular response in the rat.