Background: No cases of occupational asthma caused by the inhalation of antigens from Anisakis simplex have been published. Objective: The purpose of this study was to evaluate the possibility that A simplex can play a role in the asthma experienced by 2 workers when handling fish and fish flour. Methods: Skin prick and bronchial challenge tests with A simplex were performed. We also carried out measurements of specific IgE to A simplex and immunoblotting. Results: Both patients had strong positive skin test responses, challenge test responses, and specific IgE to A simplex . Immunoblotting showed that both patients also had IgE against several bands in the fish flour extract, suggesting contamination by Anisakis allergens. Conclusion: These 2 patients provide evidence for occupational asthma caused by A simplex , based on in vivo and in vitro tests for Anisakis-specific IgE. (J Allergy Clin Immunol 1998;102:831-4.)