Immune responses to topically applied haptens, such as 2, 4-dinitro-1-fluorobenzene (DNFB) are commonly used in vivo measures of immunity in mammals. This immune reaction has not been quantitatively studied in reptiles. Adult anoles were sensitized by topical application of DNFB in acetone. Hapten challenge was initiated by topical application of DNFB on the throat-fan. Throat-fan swelling was used to measure the subsequent reaction in vivo. Significant (p < 0.05) throat-fan swelling was present in DNFB sensitized anoles during the 4 - 36 hr post-challenge period with a peak response between 8 - 12 hr post-challenge. At 20 hr post-challenge, the reaction was histologically characterized by pronounced epidermal/dermal edema, dermal capillary dilation and clogging with leukocytes. Throat-fan swelling responses were completely dependent upon prior DNFB sensitization and could be adoptively transferred to naive animals using serum. Anoles are capable of being immunologically sensitized to topically applied haptens and respond with an Arthus-like reaction. The throat-fan swelling reaction to DNFB may be a useful, non-invasive in vivo measure of immunity in reptiles.