An animal model for the excited skin syndrome was developed in the guinea pig. Hyperirritability of the skin could be induced by immunization with Freund’s complete adjuvant (FCA). This hyperirritability was evident from the enhancement of both patch test reactions to an irritant (sodium lauryl sulfate) and open epicutaneous test reactions to a contact sensitizer (2,4-dinitrochlorobenzene). The skin tests were performed at sites other than those pretreated with FCA. Maximum enhancement was observed in a period 3–5 weeks after FCA immunization. A similar but less marked hyperirritability could be induced by eliciting a localized chronic croton oil dermatitis. The period of hyperirritability induced by FCA or croton oil was preceded by a short period (1–14 days) of depressed skin reactivity.