SummaryCertain allergic asthmatic patients exhibit a dual response in the lung following bronchial challenge with the appropriate allergen, Often this is paralleled by a cutaneous dual response when the antigen is injected intradermally. The mechanisms underlying such phenomena are not established, but some evidence suggests that the late response is a consequence of the early response. Since platelet activation has been observed following antigen challenge in asthmatic subjects, we have studied the ability of platelet activating factor (PAF‐acether. AGEPC) to induce cutaneous inflammatory responses in man. In a time course study over 24 hr, PAF‐acether produced a biphasic response: an immediate weal and flare reaction, which resolved within 1‐2 hr and was followed some 3‐6 hr later by a delayed reaction in which erythema associated with hyperaigesia was evident. These observations suggest that PAF‐acether should be considered in the context of allergic asthma as a possible mediator of the dual response to
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