SummaryPapain is a proteolytic enzyme with elastolytic activity, which produces emphysemalike lesions when introduced into the airways of animals. It is encountered by humans in numerous occupations, medications and domestic products.Sensitization to papain in two subjects in different occupations was confirmed with skin tests with chemical‐grade papain and radioallergosorbent tests (RAST), with a papain which had been chemically inactivated by selective active site blockade. Skin tests and RAST were negative in non‐symptomatic co‐workers. Withdrawal from occupational exposure to papain resulted in an improvement in symptoms.In a survey of 330 subjects at the time they were receiving routine allergy skin tests, seven reacted to papain. Sensitization was confirmed by the RAST. Serum IgG antibodies to papain were detected among sensitized individuals and also in five out of 266 sera obtained from a clinical hospital laboratory.The findings illustrate immune responses to papain in humans in the form of atopic sensitization and serum IgG antibodies. Moreover, recurrent respiratory symptoms in the presenting persons served to illustrate that they and their co‐workers were repeatedly exposed to air‐borne papain. In view of the potential danger from the proteolytic effects of papain, these observations illustrate the need for further investigations of the effects of human exposure to air‐b
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