Background: More than 400 agents are recognized as causes of occupational asthma, a work-related disease that can be induced by an immunologic or a nonimmunologic mechanism. Objective: To describe a 57-year-old man employed in the pharmaceutical industry who developed bronchial asthma while working with products such as Plantago ovata and aescin, an active ingredient with anti-inflammatory and venotonic properties. Methods: Various tests were performed, including radiography, total serum IgE titer measurements, skin tests against common pneumoallergens and Plantago species, pulmonary function studies, a methacholine test, and specific inhalation challenge with P ovata and aescin. Results: The results of these tests, including specific inhalation challenge, confirmed the diagnosis of occupational asthma due to aescin exposure, whereas the results of specific challenge with P ovata, a known cause of occupational asthma, were negative. Conclusions: Aescin may represent a new causative agent of occupational asthma in personnel working in the pharmaceutical industry. The mechanism by which aescin can produce asthma is unknown, but analysis of the characteristics of our patient suggests a non-IgE immunologic mechanism, although an irritative mechanism secondary to long-term low-level exposure to aescin, a possible irritant, cannot be ruled out.