Twenty eight workers of a pharmaceutical factory were studied. The company produced morphine and other alkaloids extracting the active principles from shells of Papaver somniferum. Six of the exposed subjects had clinical symptoms of sensitization to this allergen and positive skin tests. A bronchial provocation test was found to be positive on 4 workers and specific IgE could be found on the 6 sensitized patients by an ELISA and a RAST test using an aqueous extract of P. somniferum. A histamine release using the same antigen was also positive in the 4 samples from sensitized patients available. An SDS-PAGE of the extract revealed a major protein band with an estimated mol wt of 52,000 d. This band had the highest IgE-binding capacity as shown by immunoblotting. All these facts suggest that P. somniferum allergy is mediated by an IgE mediated mechanism and not by a pharmacological or toxic effect of the alkaloids or polyphenols.